Thorsten Brehm: GPWS: Fixed permanent blocking of lower prio warnings

Only block callouts which were actually issued to the pilot. When
multiple callouts trigger at the same time, allow lower prio warnings
to be issued once the higher prio ones are resolved.
=> Gear/flap warnings are now working reliably (no longer blocked
permanently when altitude callouts are enabled).

src/Instrumentation/mk_viii.cxx

@@ -2956,7 +2956,7 @@ MK_VIII::AlertHandler::update ()
 
   // set new state
 
-  old_alerts = alerts;
+  old_alerts = voice_alerts;
   repeated_alerts = 0;
   altitude_callout_voice = NULL;
 }