[PATCH] git-merge-one-file-script: do not misinterpret rm failure.

When a merge adds a file DF and removes a directory there by
deleting a path DF/DF, git-merge-one-file-script can be called
for the removal of DF/DF when the path DF is already created by
"git-read-tree -m -u".  When this happens, we get confused by a
failure return from 'rm -f -- "$4"' (where $4 is DF/DF); finding
file DF there the "rm -f" command complains that DF is not a
directory.

What we want to ensure is that there is no file DF/DF in this
case. Avoid getting ourselves confused by first checking if
there is a file, and only then try to remove it (and check for
failure from the "rm" command).

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