Initial minimal working tracerestrict implementation.

This is a port of the tracerestrict/routing restrictions feature
from TTDPatch.
At present this implements if tests (train length only),
and pathfinder deny and penalty actions.
This requires the use of YAPF. Note that restrictions are only evaluated
within the YAPF lookahead distance.

src/saveload/afterload.cpp

@@ -2988,6 +2988,8 @@ bool AfterLoadGame()
 	ResetSignalHandlers();
 
 	AfterLoadLinkGraphs();
+
+	AfterLoadTraceRestrict();
 	return true;
 }