Add prefix parameter to cgit_print_diff()

This allows a diff to be restricted to the path prefix specified in the url.

Signed-off-by: Lars Hjemli <hjemli@gmail.com>

cgit.c

@@ -107,7 +107,7 @@ static void cgit_print_repo_page(struct cacheitem *item)
 		cgit_print_tag(cgit_query_sha1);
 		break;
 	case CMD_DIFF:
-		cgit_print_diff(cgit_query_sha1, cgit_query_sha2);
+		cgit_print_diff(cgit_query_sha1, cgit_query_sha2, cgit_query_path);
 		break;
 	default:
 		cgit_print_error("Invalid request");