[PATCH] Teach the recursive merge strategy about renames.

It will now merge cases where a file was renamed in one branch and
modified in the other branch cleanly. We also detect a couple of
conflict cases now that wasn't detected before.

Signed-off-by: Fredrik Kuivinen <freku045@student.liu.se>
Signed-off-by: Junio C Hamano <junkio@cox.net>