Merge branch 'day_length-sx' into jgrpp

Conflicts:
	src/lang/english.txt
	src/saveload/extended_ver_sl.cpp
	src/saveload/extended_ver_sl.h
	src/timetable_cmd.cpp

src/saveload/extended_ver_sl.h

@@ -34,6 +34,7 @@ enum SlXvFeatureIndex {
 	XSLFI_VEHICLE_REPAIR_COST,                    ///< Vehicle repair costs patch
 	XSLFI_ENH_VIEWPORT_PLANS,                     ///< Enhanced viewport patch: plans
 	XSLFI_INFRA_SHARING,                          ///< Infrastructure sharing patch
+	XSLFI_VARIABLE_DAY_LENGTH,                    ///< Variable day length patch
 
 	XSLFI_SIZE,                                   ///< Total count of features, including null feature
 };