[PATCH] git-resolve-script: Add LAST_MERGE and use git-rev-parse

[PATCH] git-resolve-script: Add LAST_MERGE and use git-rev-parse

Make git-resolve-script only write MERGE_HEAD if a merge actually
occurred. All merge failures leave ORIG_HEAD and LAST_MERGE
behind (instead of ORIG_HEAD and MERGE_HEAD).

Use git-rev-parse to expand arguments (and check for bad ones).

Signed-off-by: Dan Holmsand <holmsand@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>