Fix un-inited vars found by valgrind.

All benign, but good to get fixed.

src/Aircraft/FlightHistory.cxx

@@ -70,6 +70,7 @@ void FGFlightHistory::init()
     
     // force bucket re-allocation
     m_validSampleCount = SAMPLE_BUCKET_WIDTH;
+    m_lastCaptureTime = globals->get_sim_time_sec();
 }
 
 void FGFlightHistory::shutdown()

src/Instrumentation/gps.cxx

@@ -274,6 +274,8 @@ GPS::init ()
     _realismSimpleGps->setBoolValue(true);
   }
   
+  clearOutput();
+    
   // last thing, add the deprecated prop watcher
   new DeprecatedPropListener(_gpsNode);
 }

src/Instrumentation/navradio.cxx

@@ -105,6 +105,7 @@ static std::auto_ptr<SGInterpTable> static_terminalRangeInterp,
 FGNavRadio::FGNavRadio(SGPropertyNode *node) :
     _operable(false),
     play_count(0),
+    _nav_search(true),
     _last_freq(0.0),
     target_radial(0.0),
     effective_range(0.0),