Update libgit2.
git_remote_download only takes one argument.
Update to the new clone callback structure.
Fix Rugged::Repository.discover to return a Repository object.

This is Issue #270 and I ran into this a day or so ago. It seems that when it was
implemented it was just returning the location of the repository on disk. Maybe
the this was the original intention and if that's changed I can just modify the
documentation.
Merge pull request #268 from libgit2/arthur/travis-changes

Changes to the Travis build configuration
Use tabs instead of spaces.
Merge pull request #272 from johnbellone/issue/270

Fix Rugged::Repository.discover to return a Repository object.
Merge pull request #271 from libgit2/arthur/update-libgit2

Update to the latest libgit2 changes
Use CMake when building the vendored libgit2.
Link to all libgit2 dependencies.
Specify -fPIC when we build the static lib.
Bring back support for building rugged without CMake.

But we're now printing out warnings, so people will know that Rugged
built without CMake does not correctly support some features.
Make sure that the libgit2 version we build is threadsafe.

This is especially interesting on Rubinius, where rugged/libgit2 code
can actually be executed in different threads concurrently.
Bundle files needed for building libgit2 with CMake.
Make sure we keep license files of dependencies in the bundled libgit2.
Building through CMake depends on libgit2.pc.in.
Why didn't we have a gem task before?