Add two methods to the `WP_Object_Class` class whose absence causes fatal errors in WP 3.6.

The `WP_Object_Class` implementation already leverages the data these two methods manipulate.

object-cache.php

@@ -1010,4 +1010,28 @@ class WP_Object_Cache {
 
 		return false;
 	}
+
+	/**
+	 * Sets the list of global groups.
+	 *
+	 * @param array $groups List of groups that are global.
+	 */
+	function add_global_groups( $groups ) {
+		$groups = (array) $groups;
+
+		$groups = array_fill_keys( $groups, true );
+		$this->global_groups = array_merge( $this->global_groups, $groups );
+	}
+
+	/**
+	 * Sets the list of groups not to be cached by Redis.
+	 *
+	 * @param array $groups List of groups that are to be ignored.
+	 */
+	function add_non_persistent_groups( $groups ) {
+		$groups = (array) $groups;
+
+		$groups = array_fill_keys( $groups, true );
+		$this->no_redis_groups = array_merge( $this->no_redis_groups, $groups );
+	}
 }