Pass through function to discard megolm session

To make debugging crypto slightly faster

src/client.js

@@ -702,6 +702,21 @@ MatrixClient.prototype.isRoomEncrypted = function(roomId) {
     return this._roomList.isRoomEncrypted(roomId);
 };
 
+/**
+ * Forces the current outbound group session to be discarded such
+ * that another one will be created next time an event is sent.
+ *
+ * @param roomId The ID of the room to discard the session for
+ *
+ * This should not normally be necessary.
+ */
+MatrixClient.prototype.forceDiscardSession = function(roomId) {
+    if (!this._crypto) {
+        throw new Error("End-to-End encryption disabled");
+    }
+    return this._crypto.forceDiscardSession(roomId);
+};
+
 /**
  * Get a list containing all of the room keys
  *