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/extended_ver_sl.cpp

@@ -69,6 +69,7 @@ const SlxiSubChunkInfo _sl_xv_sub_chunk_infos[] = {
 	{ XSLFI_VEH_LIFETIME_PROFIT,    XSCF_NULL,                1,   1, "veh_lifetime_profit",       NULL, NULL, NULL        },
 	{ XSLFI_LINKGRAPH_DAY_SCALE,    XSCF_NULL,                1,   1, "linkgraph_day_scale",       NULL, NULL, NULL        },
 	{ XSLFI_TEMPLATE_REPLACEMENT,   XSCF_NULL,                1,   1, "template_replacement",      NULL, NULL, "TRPL,TMPL" },
+	{ XSLFI_MORE_RAIL_TYPES,        XSCF_NULL,                1,   1, "more_rail_types",           NULL, NULL, NULL        },
 	{ XSLFI_NULL, XSCF_NULL, 0, 0, NULL, NULL, NULL, NULL },// This is the end marker
 };