Locked frame times; SAM, GUN, AGUN work again.

- all frames are 40ms long. (except something in the sidebar, which should really be PlayFetchIndex anyway)
    - SAM, GUN, and AGUN no longer crash the game when built. (Turreted used Mobile, which those buildings don't have)

OpenRa.Game/Graphics/Animation.cs

@@ -56,6 +56,11 @@ namespace OpenRa.Game.Graphics
 		int timeUntilNextFrame;
 		Action tickFunc;
 
+		public void Tick()
+		{
+			Tick( 40 ); // tick one frame
+		}
+
 		public void Tick( int t )
 		{
 			if( tickAlways )