[PATCH] Add git-verify-pack command.

Given a list of <pack>.idx files, this command validates the
index file and the corresponding .pack file for consistency.

This patch also uses the same validation mechanism in fsck-cache
when the --full flag is used.

During normal operation, sha1_file.c verifies that a given .idx
file matches the .pack file by comparing the SHA1 checksum
stored in .idx file and .pack file as a minimum sanity check.
We may further want to check the pack signature and version when
we map the pack, but that would be a separate patch.

Earlier, errors to map a pack file was not flagged fatal but led
to a random fatal error later.  This version explicitly die()s
when such an error is detected.

Signed-off-by: Junio C Hamano <junkio@cox.net>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/cache.h b/cache.h
index 9bfcdb6..9b021d6 100644
--- a/cache.h
+++ b/cache.h
@@ -246,9 +246,13 @@
 	unsigned int *index_base;
 	void *pack_base;
 	unsigned int pack_last_used;
+	unsigned int pack_use_cnt;
 	char pack_name[0]; /* something like ".git/objects/pack/xxxxx.pack" */
 } *packed_git;
 extern void prepare_packed_git(void);
+extern int use_packed_git(struct packed_git *);
+extern void unuse_packed_git(struct packed_git *);
+extern struct packed_git *add_packed_git(char *, int);
 extern int num_packed_objects(const struct packed_git *p);
 extern int nth_packed_object_sha1(const struct packed_git *, int, unsigned char*);