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

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

src/saveload/afterload.cpp

@@ -3597,6 +3597,12 @@ bool AfterLoadGame()
 		}
 	}
 
+	if (SlXvIsFeatureMissing(XSLFI_SAVEGAME_UNIQUE_ID)) {
+		/* Generate a random id for savegames that didn't have one */
+		/* We keep id 0 for old savegames that don't have an id */
+		_settings_game.game_creation.generation_unique_id = _interactive_random.Next(UINT32_MAX-1) + 1; /* Generates between [1;UINT32_MAX] */
+	}
+
 	/* Road stops is 'only' updating some caches */
 	AfterLoadRoadStops();
 	AfterLoadLabelMaps();

src/saveload/extended_ver_sl.cpp

@@ -93,6 +93,7 @@ const SlxiSubChunkInfo _sl_xv_sub_chunk_infos[] = {
 	{ XSLFI_BUY_LAND_RATE_LIMIT,    XSCF_NULL,                1,   1, "buy_land_rate_limit",       NULL, NULL, NULL        },
 	{ XSLFI_DUAL_RAIL_TYPES,        XSCF_NULL,                1,   1, "dual_rail_types",           NULL, NULL, NULL        },
 	{ XSLFI_CONSIST_SPEED_RD_FLAG,  XSCF_NULL,                1,   1, "consist_speed_rd_flag",     NULL, NULL, NULL        },
+	{ XSLFI_SAVEGAME_UNIQUE_ID,     XSCF_IGNORABLE_ALL,       1,   1, "savegame_unique_id",        NULL, NULL, NULL        },
 	{ XSLFI_NULL, XSCF_NULL, 0, 0, NULL, NULL, NULL, NULL },// This is the end marker
 };
 

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