webdav: add MKCOL support to server

carddav/server.go

@@ -268,3 +268,7 @@ func (b *backend) Put(r *http.Request) error {
 func (b *backend) Delete(r *http.Request) error {
 	panic("TODO")
 }
+
+func (b *backend) Mkcol(r *http.Request) error {
+	return internal.HTTPErrorf(http.StatusForbidden, "carddav: address book creation unsupported")
+}