added a gameframe hook

--HG--
extra : convert_revision : svn%3A39bc706e-5318-0410-9160-8a85361fbb7c/trunk%40537

plugins/include/sourcemod.inc

@@ -148,6 +148,13 @@ forward OnClientSettingsChanged(client);
  */
 forward OnClientAuthorized(client, const String:auth[]);
 
+/**
+ * Called before every server frame.  Note that you should avoid
+ * doing expensive computations here, and you should declare large
+ * local arrays using 'decl' instead of 'new'.
+ */
+forward OnGameFrame();
+
 /**
  * Returns the maximum number of clients allowed on the server.
  *