Removed the BUILD_CLAR CMake flag, and updated the readme.

This converts virtually all of the places that allocate GIT_PATH_MAX
buffers on the stack for manipulating paths to use git_buf objects
instead.  The patch is pretty careful not to touch the public API
for libgit2, so there are a few places that still use GIT_PATH_MAX.

This extends and changes some details of the git_buf implementation
to add a couple of extra functions and to make error handling easier.

This includes serious alterations to all the path.c functions, and
several of the fileops.c ones, too.  Also, there are a number of new
functions that parallel existing ones except that use a git_buf
instead of a stack-based buffer (such as git_config_find_global_r
that exists alongsize git_config_find_global).

This also modifies the win32 version of p_realpath to allocate whatever
buffer size is needed to accommodate the realpath instead of hardcoding
a GIT_PATH_MAX limit, but that change needs to be tested still.

The following files now have 0444 permissions:

- loose objects
- pack indexes
- pack files
- packs downloaded by fetch
- packs downloaded by the HTTP transport

And the following files now have 0666 permissions:

- config files
- repository indexes
- reflogs
- refs

This brings libgit2 more in line with Git.

Note that git_filebuf_commit() and git_filebuf_commit_at() have both
gained a new mode parameter.

The latter change fixes an important issue where filebufs created with
GIT_FILEBUF_TEMPORARY received 0600 permissions (due to mkstemp(3)
usage). Now we chmod() the file before renaming it into place.

Tests have been added to confirm that new commit, tag, and tree
objects are created with the right permissions. I don't have access to
Windows, so for now I've guarded the tests with "#ifndef GIT_WIN32".

To further match how Git behaves, this change makes most of the
directories libgit2 creates in a git repo have a file mode of
0777. Specifically:

- Intermediate directories created with git_futils_mkpath2file() have
  0777 permissions. This affects odb_loose, reflog, and refs.

- The top level folder for bare repos is created with 0777
  permissions.

- The top level folder for non-bare repos is created with 0755
  permissions.

- /objects/info/, /objects/pack/, /refs/heads/, and /refs/tags/ are
  created with 0777 permissions.

Additionally, the following changes have been made:

- fileops functions that create intermediate directories have grown a
  new dirmode parameter. The only exception to this is filebuf's
  lock_file(), which unconditionally creates intermediate directories
  with 0777 permissions when GIT_FILEBUF_FORCE is set.

- The test runner now sets the umask to 0 before running any
  tests. This ensurses all file mode checks are consistent across
  systems.

- t09-tree.c now does a directory permissions check. I've avoided
  adding this check to other tests that might reuse existing
  directories from the prefabricated test repos. Because they're
  checked into the repo, they have 0755 permissions.

- Other assorted directories created by tests have 0777 permissions.

 - fix retrieval of a file status when working against a newly initialized repository
 - reduce memory pressure
 - prevents a directory from being tested

Hey. Apologies in advance -- I broke your bindings.

This is a major commit that includes a long-overdue redesign of the
whole object-database structure. This is expected to be the last major
external API redesign of the library until the first non-alpha release.

Please get your bindings up to date with these changes. They will be
included in the next minor release. Sorry again!

Major features include:

	- Real caching and refcounting on parsed objects
	- Real caching and refcounting on objects read from the ODB
	- Streaming writes & reads from the ODB
	- Single-method writes for all object types
	- The external API is now partially thread-safe

The speed increases are significant in all aspects, specially when
reading an object several times from the ODB (revwalking) and when
writing big objects to the ODB.

Here's a full changelog for the external API:

blob.h
------

	- Remove `git_blob_new`
	- Remove `git_blob_set_rawcontent`
	- Remove `git_blob_set_rawcontent_fromfile`
	- Rename `git_blob_writefile` -> `git_blob_create_fromfile`
	- Change `git_blob_create_fromfile`:
		The `path` argument is now relative to the repository's working dir
	- Add `git_blob_create_frombuffer`

commit.h
--------

	- Remove `git_commit_new`
	- Remove `git_commit_add_parent`
	- Remove `git_commit_set_message`
	- Remove `git_commit_set_committer`
	- Remove `git_commit_set_author`
	- Remove `git_commit_set_tree`

	- Add `git_commit_create`
	- Add `git_commit_create_v`
	- Add `git_commit_create_o`
	- Add `git_commit_create_ov`

tag.h
-----

	- Remove `git_tag_new`
	- Remove `git_tag_set_target`
	- Remove `git_tag_set_name`
	- Remove `git_tag_set_tagger`
	- Remove `git_tag_set_message`

	- Add `git_tag_create`
	- Add `git_tag_create_o`

tree.h
------

	- Change `git_tree_entry_2object`:
		New signature is `(git_object **object_out, git_repository *repo, git_tree_entry *entry)`

	- Remove `git_tree_new`
	- Remove `git_tree_add_entry`
	- Remove `git_tree_remove_entry_byindex`
	- Remove `git_tree_remove_entry_byname`
	- Remove `git_tree_clearentries`
	- Remove `git_tree_entry_set_id`
	- Remove `git_tree_entry_set_name`
	- Remove `git_tree_entry_set_attributes`

object.h
------------

	- Remove `git_object_new
	- Remove `git_object_write`

	- Change `git_object_close`:
		This method is now *mandatory*. Not closing an object causes a
		memory leak.

odb.h
-----

	- Remove type `git_rawobj`
	- Remove `git_rawobj_close`
	- Rename `git_rawobj_hash` -> `git_odb_hash`
	- Change `git_odb_hash`:
		New signature is `(git_oid *id, const void *data, size_t len, git_otype type)`

	- Add type `git_odb_object`
	- Add `git_odb_object_close`

	- Change `git_odb_read`:
		New signature is `(git_odb_object **out, git_odb *db, const git_oid *id)`
	- Change `git_odb_read_header`:
		New signature is `(size_t *len_p, git_otype *type_p, git_odb *db, const git_oid *id)`
	- Remove `git_odb_write`
	- Add `git_odb_open_wstream`
	- Add `git_odb_open_rstream`

odb_backend.h
-------------

	- Change type `git_odb_backend`:
		New internal signatures are as follows

			int (* read)(void **, size_t *, git_otype *, struct git_odb_backend *, const git_oid *)
			int (* read_header)(size_t *, git_otype *, struct git_odb_backend *, const git_oid *)
			int (* writestream)(struct git_odb_stream **, struct git_odb_backend *, size_t, git_otype)
			int (* readstream)( struct git_odb_stream **, struct git_odb_backend *, const git_oid *)

	- Add type `git_odb_stream`
	- Add enum `git_odb_streammode`

Signed-off-by: Vicent Marti <tanoku@gmail.com>

add actual must_pass calls back into the repo tests and remove ./ from
beginning of temp repo path

Tests are now declared with detailed descriptions and a short test name:

	BEGIN_TEST(the_test0, "this is an example test that does something")
		...
	END_TEST

Modules are declared through a simple macro interface:

	BEGIN_MODULE(mod_name)
		ADD_TEST(the_test0);
		...
	END_MODULE

Error messages when tests fail have been greatly improved.

Signed-off-by: Vicent Marti <tanoku@gmail.com>