Add plain patch view

The new view mimics the output from `git format-patch`, making it possible
to cherry-pick directly from cgit with something like `curl $url | git am`.

Inspired by a patch to `git-apply` by Mike Hommey:
  http://thread.gmane.org/gmane.comp.version-control.git/67611/focus=67610

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

cgit.c

@@ -75,6 +75,11 @@ static void cgit_print_repo_page(struct cacheitem *item)
 		return;
 	}
 
+	if (cgit_cmd == CMD_PATCH) {
+		cgit_print_patch(cgit_query_sha1, item);
+		return;
+	}
+
 	if (cgit_cmd == CMD_BLOB) {
 		cgit_print_blob(item, cgit_query_sha1, cgit_query_path);
 		return;