[PATCH] Make sure git-resolve-script always works on commits

[PATCH] Make sure git-resolve-script always works on commits

You can resolve a tag, and it does the right thing except that it might
end up writing the tag itself into the resulting HEAD, which will confuse
subsequent operations no end.

This makes sure that when we resolve two heads, we will have turned them
into proper commits before we start acting on them.

This also fixes the parsing of "treeish^0", which would incorrectly
resolve to "treeish" instead of causing an error.

Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>