added helper function for panel text

--HG--
extra : convert_revision : svn%3A39bc706e-5318-0410-9160-8a85361fbb7c/trunk%401367

plugins/include/menus.inc

@@ -644,6 +644,20 @@ native bool:SetPanelKeys(Handle:panel, keys);
  */
 native bool:SendPanelToClient(Handle:panel, client, MenuHandler:handler, time);
 
+/**
+ * @brief Returns the amount of text the menu can still hold.  If this is 
+ * limit is reached or overflowed, the text is silently truncated.  
+ *
+ * Radio menus: Currently 511 characters (512 bytes).
+ * Valve menus: Currently -1 (no meaning).
+ *
+ * @param panel			A MenuPanel Handle.
+ * @return				Number of characters that the menu can still hold, 
+ *						or -1 if there is no known limit.
+ * @error				Invalid Handle.
+ */
+native GetPanelTextRemaining(Handle:panel);
+
 /**
  * @brief Returns the current key position.
  *