Fix some gcc warnings

src/Instrumentation/navradio.cxx

@@ -897,7 +897,8 @@ void FGNavRadio::updateAudio()
   }
   
   last_time = now;
-  play_count = ++play_count % NUM_IDENT_SLOTS;
+  play_count++;
+  play_count %= NUM_IDENT_SLOTS;
     
   // Previous ident is out of time;  if still playing, cut it off:
   _sgr->stop( nav_fx_name );

src/Main/bootstrap.cxx

@@ -71,10 +71,10 @@ bool free_hostname = false;
 void fgExitCleanup();
 
 static bool fpeAbort = false;
-static void handleFPE(int);
 static void initFPE();
 
 #if defined(HAVE_FEENABLEEXCEPT)
+static void handleFPE(int);
 static void
 initFPE ()
 {
@@ -115,10 +115,6 @@ handleFPE (int num)
   SG_LOG(SG_GENERAL, SG_ALERT, "Floating point interrupt (SIGFPE)");
 }
 #else
-static void handleFPE(int)
-{
-}
-
 static void initFPE()
 {
 }

src/Navaids/awynet.cxx

@@ -317,7 +317,7 @@ void FGAirwayNetwork::load(const SGPath& path)
 int FGAirwayNetwork::findNearestNode(const SGGeod& aPos)
 {
   double minDist = HUGE_VAL;
-  int index;
+  int index = -1;
   SGVec3d cart = SGVec3d::fromGeod(aPos);
   
   //cerr << "Lat " << lat << " lon " << lon << endl;

src/Traffic/Schedule.cxx

@@ -221,7 +221,7 @@ bool FGAISchedule::update(time_t now, const SGVec3d& userCart)
     // Check if this aircraft has been released. 
     FGTrafficManager *tmgr = (FGTrafficManager *) globals->get_subsystem("Traffic Manager");
     if (tmgr->isReleased(AIManagerRef)) {
-      AIManagerRef = NULL;
+      AIManagerRef = 0;
     } else {
       return true; // in visual range, let the AIManager handle it
     }