Fix regressions.

OpenRA.Game/Traits/Player/TechTreeCache.cs

@@ -26,9 +26,6 @@ namespace OpenRA.Traits
 
 			public void Tick( Player owner, Cache<string, List<Actor>> buildings )
 			{
-				// HACK
-				return;
-				
 				var effectivePrereq = prerequisites.Where( a => a.Traits.Get<BuildableInfo>().Owner.Contains( owner.Country.Race ) );
 				var nowHasPrerequisites = effectivePrereq.Any() &&
 					effectivePrereq.All( a => buildings[ a.Name ].Any( b => !b.traits.Get<Building>().Disabled ) );