Running "git commit" in core and xml touches .git/index and
.git/modules/library/xml/index, respectively, so if neither of those have
changed, neither has the git information we care about, so avoid running git
entirely (which can be slow sometimes).
The length here was previously determined automatically, and jumped from 7 to 8
recently, breaking devel/check-release. Since Git seems to think 8 characters is
better now, specify it explicitly to avoid future breakages.
git is run every time 'make' is run, but the generated include file
is only updated when necessary. Plugins will be loaded successfully
if their DFHack version matches core's (assuming OpenLibrary()
succeeds), but will produce a warning if their git commit doesn't
match core's.
lethosor