Add NewGRF railtype flag to disable realistic braking for vehs of that type

See: #242

src/newgrf.h

@@ -117,6 +117,7 @@ enum Action0RemapPropertyIds {
 	A0RPI_BRIDGE_AVAILABILITY_FLAGS,
 	A0RPI_RAILTYPE_ENABLE_PROGRAMMABLE_SIGNALS,
 	A0RPI_RAILTYPE_ENABLE_RESTRICTED_SIGNALS,
+	A0RPI_RAILTYPE_DISABLE_REALISTIC_BRAKING,
 	A0RPI_ROADTYPE_EXTRA_FLAGS,
 };