Fix gitk error running with release candidate versions of Git
After building from a tarball generated with git archive, git version
emits v1.7.4-rc1, resulting in "expected version number" errors from
gitk.
Meanwhile, after building from a git checkout or a tarball generated
with "make dist", the version is v1.7.4.rc1, which gitk accepts.
Confusing.
[jn: changelog entries tweaked based on later discussion]
Signed-off-by: Anders Kaseorg <andersk@mit.edu>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>