This change:
* Stops running tests under Go 1.1 and Go 1.2, since Travis no longer
supports them.
* Stops running tests under Go tip. Go 1.8+ requires runtime.KeepAlive()
to keep some of the references alive across CGo invocations, but that
was introduced in Go 1.7, and that would break older Go versions.
* Fixes a formatting bug that was breaking under newer Go releases.
* Uprevs libgit (test) to v0.24.6.
We have our own libgit2 in a submodule, so this is unnecessary. While in
the area, update which version of libgit2 would be downloaded and remove
unnecessary CMake flags.
lhchavez
Carlos Martín Nieto