Add setting for linkgraph times to be in non daylength scaled days.

Savegame format change for link graph jobs.
Change link graph scheduler to support more than one operation
per day, on _date_fract ticks other than SPAWN_JOIN_TICK.

src/saveload/extended_ver_sl.h

@@ -41,6 +41,7 @@ enum SlXvFeatureIndex {
 	XSLFI_EXTRA_LARGE_MAP,                        ///< Extra large map
 	XSLFI_REVERSE_AT_WAYPOINT,                    ///< Reverse at waypoint orders
 	XSLFI_VEH_LIFETIME_PROFIT,                    ///< Vehicle lifetime profit patch
+	XSLFI_LINKGRAPH_DAY_SCALE,                    ///< Linkgraph job duration & interval may be in non-scaled days
 
 	XSLFI_RIFF_HEADER_60_BIT,                     ///< Size field in RIFF chunk header is 60 bit
 	XSLFI_HEIGHT_8_BIT,                           ///< Map tile height is 8 bit instead of 4 bit, but savegame version may be before this became true in trunk