Needed because generating a target paths will add another slash.
This fixes e.g. "git-mv file dir/", which removed "file" from
version control by renaming it to "dir//file", as
git-update-index does not accept such paths.
Thanks goes to Ben Lau for noting this bug.
Signed-off-by: Josef Weidendorfer <Josef.Weidendorfer@gmx.de> Signed-off-by: Junio C Hamano <junkio@cox.net>