builtin/fetch-pack: add --refetch option

Add a refetch option to fetch-pack to force a full fetch. Use when
applying a new partial clone filter to refetch all matching objects.

Signed-off-by: Robert Coup <robert@coup.net.nz>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/fetch-pack.c

@@ -153,6 +153,10 @@ int cmd_fetch_pack(int argc, const char **argv, const char *prefix)
 			args.from_promisor = 1;
 			continue;
 		}
+		if (!strcmp("--refetch", arg)) {
+			args.refetch = 1;
+			continue;
+		}
 		if (skip_prefix(arg, ("--" CL_ARG__FILTER "="), &arg)) {
 			parse_list_objects_filter(&args.filter_options, arg);
 			continue;