Add "-l" flag for repacking only local packs

Add "-l" flag for repacking only local packs

This uses the new "--local" flag to git-pack-objects.  It currently only
makes a difference together with "-a", since a normal incremental repack
won't pack any packed objects at all (whether local or remote).

Eventually, it might end up skipping any objects that aren't local to
the current object directory, but for now it only knows to skip packed
objects.

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