Add support for commitdiff via h parameter

The commitdiff will be generated against the first parent, and the
diff page also gets the benefit of repo.defbranch.

Cleaned up some bad whitespace in cgit.h while at it.

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

cgit.c

@@ -120,7 +120,8 @@ static void cgit_print_repo_page(struct cacheitem *item)
 	} else if (!strcmp(cgit_query_page, "view")) {
 		cgit_print_view(cgit_query_sha1, cgit_query_path);
 	} else if (!strcmp(cgit_query_page, "diff")) {
-		cgit_print_diff(cgit_query_sha1, cgit_query_sha2, cgit_query_path);
+		cgit_print_diff(cgit_query_head, cgit_query_sha1, cgit_query_sha2,
+				cgit_query_path);
 	} else {
 		cgit_print_error("Invalid request");
 	}