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/command.cpp

@@ -198,6 +198,8 @@ CommandProc CmdSetTimetableStart;
 
 CommandProc CmdOpenCloseAirport;
 
+CommandProc CmdProgramSignalTraceRestrict;
+
 #define DEF_CMD(proc, flags, type) {proc, #proc, (CommandFlags)flags, type}
 
 /**
@@ -354,6 +356,8 @@ static const Command _command_proc_table[] = {
 	DEF_CMD(CmdSetTimetableStart,                              0, CMDT_ROUTE_MANAGEMENT      ), // CMD_SET_TIMETABLE_START
 
 	DEF_CMD(CmdOpenCloseAirport,                               0, CMDT_ROUTE_MANAGEMENT      ), // CMD_OPEN_CLOSE_AIRPORT
+
+	DEF_CMD(CmdProgramSignalTraceRestrict,                     0, CMDT_OTHER_MANAGEMENT      ), // CMD_PROGRAM_TRACERESTRICT_SIGNAL
 };
 
 /*!