Add generic mechanism to cross-ref settings at load time.

This is useful for loading settings from legacy/special versions,
where the corresponding setting is somewhere else and/or a PATX setting,
with duplicating all the info.
Use this to load SpringPP settings which have a corresponding setting.

src/table/settings.ini

@@ -81,6 +81,7 @@ SDT_OMANY  =  SDT_OMANY($base, $var, $type, $flags, $guiflags, $def,
 SDT_STR    =    SDT_STR($base, $var, $type, $flags, $guiflags, $def,                              $str, $strhelp, $strval, $proc, $from, $to,        $cat, $extver, $patxname),
 SDT_VAR    =    SDT_VAR($base, $var, $type, $flags, $guiflags, $def,       $min, $max, $interval, $str, $strhelp, $strval, $proc, $from, $to,        $cat, $extver, $patxname),
 SDT_NULL   =   SDT_NULL($length, $from, $to, $extver),
+SDT_XREF     = SDT_XREF(         $from, $to, $extver, $xref),
 SDT_END    = SDT_END()
 
 [defaults]
@@ -97,6 +98,7 @@ to       = SL_MAX_VERSION
 cat      = SC_ADVANCED
 extver   = {}
 patxname = NULL
+xref     = <this parameter must be set>
 
 
 
@@ -335,22 +337,12 @@ min      = 0
 max      = 3
 cat      = SC_BASIC
 
-[SDT_BOOL]
-base     = GameSettings
-var      = order.timetable_automated
-def      = true
-str      = STR_CONFIG_SETTING_TIMETABLE_AUTOMATED
-strhelp  = STR_CONFIG_SETTING_TIMETABLE_AUTOMATED_HELPTEXT
-cat      = SC_EXPERT
+[SDT_XREF]
+xref     = ""order.timetable_automated""
 extver   = SlXvFeatureTest(XSLFTO_AND, XSLFI_SPRINGPP)
 
-[SDT_BOOL]
-base     = GameSettings
-var      = order.timetable_separation
-def      = true
-str      = STR_CONFIG_SETTING_TIMETABLE_SEPARATION
-strhelp  = STR_CONFIG_SETTING_TIMETABLE_SEPARATION_HELPTEXT
-cat      = SC_EXPERT
+[SDT_XREF]
+xref     = ""order.timetable_separation""
 extver   = SlXvFeatureTest(XSLFTO_AND, XSLFI_SPRINGPP)
 
 [SDT_BOOL]
@@ -616,9 +608,8 @@ from     = 0
 cat      = SC_BASIC
 patxname = ""signal_tunnel_bridge.construction.simulated_wormhole_signals""
 
-;; construction.maximum_signal_evaluations
-[SDT_NULL]
-length   = 2
+[SDT_XREF]
+xref     = ""construction.maximum_signal_evaluations""
 extver   = SlXvFeatureTest(XSLFTO_AND, XSLFI_SPRINGPP)
 
 ;; construction.longbridges
@@ -682,9 +673,8 @@ def      = true
 str      = STR_CONFIG_SETTING_ALLOW_TOWN_ROADS
 strhelp  = STR_CONFIG_SETTING_ALLOW_TOWN_ROADS_HELPTEXT
 
-;; economy.town_cargo_factor
-[SDT_NULL]
-length   = 1
+[SDT_XREF]
+xref     = ""economy.town_cargo_factor""
 extver   = SlXvFeatureTest(XSLFTO_AND, XSLFI_SPRINGPP)
 
 [SDT_VAR]
@@ -1254,6 +1244,10 @@ strhelp  = STR_CONFIG_SETTING_PLANE_CRASHES_HELPTEXT
 strval   = STR_CONFIG_SETTING_PLANE_CRASHES_NONE
 cat      = SC_BASIC
 
+[SDT_XREF]
+xref     = ""vehicle.improved_breakdowns""
+extver   = SlXvFeatureTest(XSLFTO_AND, XSLFI_SPRINGPP)
+
 [SDT_BOOL]
 base     = GameSettings
 var      = vehicle.improved_breakdowns
@@ -1262,11 +1256,6 @@ def      = false
 str      = STR_CONFIG_SETTING_IMPROVED_BREAKDOWNS
 patxname = ""improved_breakdowns.vehicle.improved_breakdowns""
 
-;; vehicle.improved_breakdowns
-[SDT_NULL]
-length   = 1
-extver   = SlXvFeatureTest(XSLFTO_AND, XSLFI_SPRINGPP)
-
 ; station.join_stations
 [SDT_NULL]
 length   = 1
@@ -1579,9 +1568,8 @@ strhelp  = STR_CONFIG_SETTING_FEEDER_PAYMENT_SHARE_HELPTEXT
 strval   = STR_CONFIG_SETTING_PERCENTAGE
 cat      = SC_EXPERT
 
-;; economy.day_length_factor
-[SDT_NULL]
-length   = 1
+[SDT_XREF]
+xref     = ""economy.day_length_factor""
 extver   = SlXvFeatureTest(XSLFTO_AND, XSLFI_SPRINGPP)
 
 ;; economy.price_mult[0-70]
@@ -1599,11 +1587,17 @@ extver   = SlXvFeatureTest(XSLFTO_AND, XSLFI_SPRINGPP)
 length   = 16
 extver   = SlXvFeatureTest(XSLFTO_AND, XSLFI_SPRINGPP)
 
-;; economy.pay_for_repair
-;; economy.repair_cost
+[SDT_XREF]
+xref     = ""vehicle.pay_for_repair""
+extver   = SlXvFeatureTest(XSLFTO_AND, XSLFI_SPRINGPP)
+
+[SDT_XREF]
+xref     = ""vehicle.repair_cost""
+extver   = SlXvFeatureTest(XSLFTO_AND, XSLFI_SPRINGPP)
+
 ;; economy.town_consumption_rate
 [SDT_NULL]
-length   = 3
+length   = 1
 extver   = SlXvFeatureTest(XSLFTO_AND, XSLFI_SPRINGPP)
 
 ;; economy.town_pop_*
@@ -1673,19 +1667,41 @@ from     = 77
 def      = true
 cat      = SC_EXPERT
 
-;; economy.infrastructure_sharing[0-3]
-[SDT_NULL]
-length   = 4
+
+[SDT_XREF]
+xref     = ""economy.infrastructure_sharing[0]""
 extver   = SlXvFeatureTest(XSLFTO_AND, XSLFI_SPRINGPP)
 
-;; economy.sharing_fee[0-3]
-[SDT_NULL]
-length   = 16
+[SDT_XREF]
+xref     = ""economy.infrastructure_sharing[1]""
 extver   = SlXvFeatureTest(XSLFTO_AND, XSLFI_SPRINGPP)
 
-;; economy.sharing_payment_in_debt
-[SDT_NULL]
-length   = 1
+[SDT_XREF]
+xref     = ""economy.infrastructure_sharing[2]""
+extver   = SlXvFeatureTest(XSLFTO_AND, XSLFI_SPRINGPP)
+
+[SDT_XREF]
+xref     = ""economy.infrastructure_sharing[3]""
+extver   = SlXvFeatureTest(XSLFTO_AND, XSLFI_SPRINGPP)
+
+[SDT_XREF]
+xref     = ""economy.sharing_fee[0]""
+extver   = SlXvFeatureTest(XSLFTO_AND, XSLFI_SPRINGPP)
+
+[SDT_XREF]
+xref     = ""economy.sharing_fee[1]""
+extver   = SlXvFeatureTest(XSLFTO_AND, XSLFI_SPRINGPP)
+
+[SDT_XREF]
+xref     = ""economy.sharing_fee[2]""
+extver   = SlXvFeatureTest(XSLFTO_AND, XSLFI_SPRINGPP)
+
+[SDT_XREF]
+xref     = ""economy.sharing_fee[3]""
+extver   = SlXvFeatureTest(XSLFTO_AND, XSLFI_SPRINGPP)
+
+[SDT_XREF]
+xref     = ""economy.sharing_payment_in_debt""
 extver   = SlXvFeatureTest(XSLFTO_AND, XSLFI_SPRINGPP)
 
 [SDT_VAR]