Make 32 instead of 16 rail types possible. by using one free bit of m1 in the map array.

(cherry picked from commit b44843800880cdc186f5183301ee0f42afbb5f84)

Also set non-rail type M3 bits to 0 where applicable.
Change savegame versioning to SLXI format.

src/saveload/afterload.cpp

@@ -3213,6 +3213,19 @@ bool AfterLoadGame()
 		FOR_ALL_VEHICLES(v) v->profit_lifetime = 0;
 	}
 
+	// Before this version we didn't store the 5th bit of the tracktype here.
+	// So set it to 0 just in case there was garbage in there.
+	if (SlXvIsFeatureMissing(XSLFI_MORE_RAIL_TYPES)) {
+		for (TileIndex t = 0; t < map_size; t++) {
+			if (_m[t].type == MP_RAILWAY ||
+					_m[t].type == MP_ROAD ||
+					_m[t].type == MP_STATION ||
+					_m[t].type == MP_TUNNELBRIDGE) {
+				SB(_m[t].m1, 7, 1, 0);
+			}
+		}
+	}
+
 	/* Road stops is 'only' updating some caches */
 	AfterLoadRoadStops();
 	AfterLoadLabelMaps();