Use off_t for index and pack file lengths.

Since the index_size and pack_size members of struct packed_git
are the lengths of those corresponding files we should use the
off_t size of the operating system to store these file lengths,
rather than an unsigned long.  This would help in the future should
we ever resurrect Junio's 64 bit index implementation.
Signed-off-by: NShawn O. Pearce <spearce@spearce.org>
Signed-off-by: NJunio C Hamano <junkio@cox.net>

cache.h

@@ -347,10 +347,10 @@ struct pack_window {
 
 extern struct packed_git {
 	struct packed_git *next;
-	unsigned long index_size;
-	unsigned long pack_size;
 	struct pack_window *windows;
 	unsigned int *index_base;
+	off_t index_size;
+	off_t pack_size;
 	int pack_local;
 	unsigned char sha1[20];
 	/* something like ".git/objects/pack/xxxxx.pack" */