Avoid 'Only variables should be passed by reference' warnings. Reverts [18110]. see #18975

git-svn-id: http://svn.automattic.com/wordpress/trunk@18998 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/wp-db.php

@@ -1369,7 +1369,7 @@ class wpdb {
 			// Return an array of row objects with keys from column 1
 			// (Duplicates are discarded)
 			foreach ( $this->last_result as $row ) {
-				$key = array_shift( get_object_vars( $row ) );
+				$key = array_shift( $var_by_ref = get_object_vars( $row ) );
 				if ( ! isset( $new_array[ $key ] ) )
 					$new_array[ $key ] = $row;
 			}