Nico pointed out that having verify_pack.c and verify-pack.c was
confusing.  Rename verify_pack.c to pack-check.c as suggested,
and enhances the verification done quite a bit.

 - Built-in sha1_file unpacking knows that a base object of a
   deltified object _must_ be in the same pack, and takes
   advantage of that fact.

 - Earlier verify-pack command only checked the SHA1 sum for the
   entire pack file and did not look into its contents.  It now
   checks everything idx file claims to have unpacks correctly.

 - It now has a hook to give more detailed information for
   objects contained in the pack under -v flag.

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