Fix detection of the Sufami Turbo base cartridge.

The Sufami Turbo base cartridge is listed in the Super Famicom verified dump
database, so it did not use the heuristics. It turns out the heuristic detection
wouldn't have worked anyway - although the game's header does contain the serial
A9PJ, the heuristic revision() method does not report that serial at all.

Meanwhile, the serial A9PJ is *also* used by the game Bishoujo Senshi Sailor
Moon SuperS - Fuwafuwa Panic, so loading this game would prompt for Sufami Turbo
mini-cartridges even though the game could not make use of them.

Fixes #323

bsnes/heuristics/super-famicom.cpp

@@ -266,6 +266,13 @@ auto SuperFamicom::board() const -> string {
     if(headerAddress == 0x40ffb0) mode = "EXHIROM-";
   }
 
+  //the Sufami Turbo has the non-descriptive label "ADD-ON BASE CASSETE"
+  //(yes, missing a T), and its serial "A9PJ" is shared with
+  //Bishoujo Senshi Sailor Moon SuperS - Fuwafuwa Panic (Japan)
+  //so we identify it with this embedded string
+  string sufamiSignature = "BANDAI SFC-ADX";
+  if (string(data.view(0, sufamiSignature.length())) == sufamiSignature) board.append("ST-", mode);
+
   //this game's title ovewrites the map mode with '!' (0x21), but is a LOROM game
   if(title() == "YUYU NO QUIZ DE GO!GO") mode = "LOROM-";
 
@@ -274,10 +281,7 @@ auto SuperFamicom::board() const -> string {
   bool epsonRTC = false;
   bool sharpRTC = false;
 
-         if(serial() == "A9PJ") {
-  //Sufami Turbo (JPN)
-    board.append("ST-", mode);
-  } else if(serial() == "ZBSJ") {
+  if(serial() == "ZBSJ") {
   //BS-X: Sore wa Namae o Nusumareta Machi no Monogatari (JPN)
     board.append("BS-MCC-");
   } else if(serial() == "042J") {