The code in this branch has been modified so it works with the global
state introduced in development.

Do not add the `git2` path to internal includes, or that will cause
an extra path dependency.

That makes more sense to me.

See `global.c` for a description of what we're doing.

When libgit2 is built with GIT_THREADS support, the threading system
must be explicitly initialized with `git_threads_init()`.

This new version of the references code is significantly faster and
hopefully easier to read.

External API stays the same. A new method `git_reference_reload()` has
been added to force updating a memory reference from disk. In-memory
references are no longer updated automagically -- this was killing us.

If a reference is deleted externally and the user doesn't reload the
memory object, nothing critical happens: any functions using that
reference should fail gracefully (e.g. deletion, renaming, and so on).

All generated references from the API are read only and must be free'd
by the user. There is no reference counting and no traces of generated
references are kept in the library.

There is no longer an internal representation for references. There is
only one reference struct `git_reference`, and symbolic/oid targets are
stored inside an union.

Packfile references are stored using an optimized struct with flex array
for reference names. This should significantly reduce the memory cost of
loading the packfile from disk.

Currently libgit2 shares pointers to its internal reference cache with
the user. This leads to several problems like invalidation of reference
pointers when reordering the cache or manipulation of the cache from
user side.

Give each user its own git_reference instead of leaking the internal
representation (struct reference).

Add the following new API functions:

	* git_reference_free
	* git_reference_is_packed

Signed-off-by: schu <schu-github@schulog.org>

Don't make git_errno static and add an argument to
git_error_print_stack. If this argument is NULL, it will print the
default stack; otherwise it will print the given stack.

Signed-off-by: Carlos Martín Nieto <carlos@cmartin.tk>

Ensure that all memory related functions (malloc, calloc, strdup, free,
etc) are using their respective `git__` wrappers.