This fixes the examples so they will build and adds a PROFILE
option to the CMakeFile that enabled gprof info on non-Windows

Use giterr_last() and make sure it's not NULL.

Add a fetch refspec arguemnt and make the arguments (name, url,
refspec), as that order makes more sense.

Conflicts:
	.travis.yml
	include/git2/diff.h
	src/config_file.c
	src/diff.c
	src/diff_output.c
	src/mwindow.c
	src/path.c
	tests-clar/clar_helpers.c
	tests-clar/object/tree/frompath.c
	tests/t00-core.c
	tests/t03-objwrite.c
	tests/t08-tag.c
	tests/t10-refs.c
	tests/t12-repo.c
	tests/t18-status.c
	tests/test_helpers.c
	tests/test_main.c

Currently, git_remote_disconnect not only closes the connection but also
frees the underlying transport object, making it impossible to write
code like

	// fetch stuff
	git_remote_download()

	// close connection
	git_remote_disconnect()

	// call user provided callback for each ref
	git_remote_update_tips(remote, callback)

because remote->refs points to references owned by the transport object.
This means, we have an idling connection while running the callback for
each reference.

Instead, allow immediate disconnect and free the transport later in
git_remote_free().

This allows the caller to update an internal structure or update the
user output with the tips that were updated.

While in the area, only try to update the ref if the value is
different from its old one.

This allows us to give updates on how it's doing