[PATCH] Implement git-checkout-cache -u to update stat information in the cache.

[PATCH] Implement git-checkout-cache -u to update stat information in the cache.

With -u flag, git-checkout-cache picks up the stat information
from newly created file and updates the cache.  This removes the
need to run git-update-cache --refresh immediately after running
git-checkout-cache.

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