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.
This patch fixes the setup stage of the config tests to notice when
the writes fail (eg $PWD is a read-only filesystem) and to correctly
skip the entire test function as a result.