Merge remote-tracking branch 'damfr/save-unique-id' into jgrpp

# Conflicts:
#	src/saveload/afterload.cpp
#	src/saveload/saveload.cpp

src/saveload/extended_ver_sl.h

@@ -67,6 +67,7 @@ enum SlXvFeatureIndex {
 	XSLFI_BUY_LAND_RATE_LIMIT,                    ///< Buy land rate limit
 	XSLFI_DUAL_RAIL_TYPES,                        ///< Two rail-types per tile
 	XSLFI_CONSIST_SPEED_RD_FLAG,                  ///< Consist speed reduction flag
+	XSLFI_SAVEGAME_UNIQUE_ID,                     ///< Savegame unique ID
 
 	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