Make the random seed controllable

- This allows eliminating random seed differences from savestates (may
be useful for some forms of sync stability testing).
- Would also allow (re)recording with randomization enabled, as the
seed can be set portably).

snes/interface/interface.cpp

@@ -22,4 +22,8 @@ time_t Interface::currentTime() {
   return time(0);
 }
 
+time_t Interface::randomSeed() {
+  return time(0);
+}
+
 }

snes/interface/interface.hpp

@@ -6,6 +6,7 @@ struct Interface {
   virtual string path(Cartridge::Slot::e slot, const string &hint) = 0;
   virtual void message(const string &text);
   virtual time_t currentTime();
+  virtual time_t randomSeed();
 };
 
 extern Interface *interface;

snes/system/system.cpp

@@ -147,7 +147,7 @@ void System::unload() {
 }
 
 void System::power() {
-  random.seed((unsigned)time(0));
+  random.seed((unsigned)interface->randomSeed());
 
   region = config.region;
   expansion = config.expansion_port;