make "index-pack" a built-in

This required some fairly trivial packfile function 'const' cleanup,
since the builtin commands get a const char *argv[] array.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git.c

@@ -320,6 +320,7 @@ static void handle_internal_command(int argc, const char **argv)
 		{ "grep", cmd_grep, USE_PAGER },
 		{ "hash-object", cmd_hash_object },
 		{ "help", cmd_help },
+		{ "index-pack", cmd_index_pack },
 		{ "init", cmd_init_db },
 		{ "init-db", cmd_init_db },
 		{ "log", cmd_log, RUN_SETUP | USE_PAGER },