Fix some more unitialized value warnings.

src/ATCDCL/ATC.hxx

@@ -65,6 +65,8 @@ enum plane_type {
 // PlaneRec - a structure holding ATC-centric details of planes under control
 // This might move or change eventually
 struct PlaneRec {
+        PlaneRec() : type(UNKNOWN), squawkcode(0) {}
+        PlaneRec(const std::string& s) : type(UNKNOWN), callsign(s), squawkcode(0) {}
 	plane_type type;
 	std::string callsign;
 	int squawkcode;

src/ATCDCL/atis.cxx

@@ -63,10 +63,9 @@ using boost::ref;
 using boost::tie;
 
 FGATIS::FGATIS() :
-  transmission(""),
-  trans_ident(""),
   old_volume(0),
   atis_failed(false),
+  msg_OK(0),
   attention(0),
   _prev_display(0),
   refname("atis")

src/Instrumentation/gps.cxx

@@ -219,6 +219,7 @@ GPS::GPS ( SGPropertyNode *node) :
   _mode("init"),
   _name(node->getStringValue("name", "gps")),
   _num(node->getIntValue("number", 0)),
+  _searchResultsCached(false),
   _computeTurnData(false),
   _anticipateTurn(false),
   _inTurn(false)