count-objects: recognize .bitmap in garbage-checking

Count-objects will report any "garbage" files in the packs
directory, including files whose extensions it does not
know (case 1), and files whose matching ".pack" file is
missing (case 2).  Without having learned about ".bitmap"
files, the current code reports all such files as garbage
(case 1), even if their pack exists. Instead, they should be
treated as case 2.
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

sha1_file.c

@@ -1194,6 +1194,7 @@ static void prepare_packed_git_one(char *objdir, int local)
 
 		if (has_extension(de->d_name, ".idx") ||
 		    has_extension(de->d_name, ".pack") ||
+		    has_extension(de->d_name, ".bitmap") ||
 		    has_extension(de->d_name, ".keep"))
 			string_list_append(&garbage, path);
 		else