libgit2 0.18.0 "Big Ben"

This is the last minor release before 1.0preview1.

Highlights of this release include:

- Branch API
- Checkout head, index and tree
- Finished clone support
- Abstracted reference API to use custom backends
- Full diff support
- New (faster) packbuilder
- Push support
- New Remotes API
- Revparse support (single and range commits)
- Stash support
- Submodules support

As always, the full changelog is available at:

	http://libgit2.github.com/libgit2/#p/changelog

Yeah, it's a huge release. Releasing stuff sucks.
Expect 1.0 and API freeze in less than a month.

Your faithful maintainer,
	 vmg

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