Minor comment fixes

src/Airports/airport.cxx

@@ -724,7 +724,7 @@ void FGAirport::validateILSData()
     
   SGPath path;
   if (!XMLLoader::findAirportData(ident(), "ils", path)) {
-    return; // no XML tower data
+    return; // no XML ILS data
   }
   
   try {

src/Navaids/NavDataCache.cxx

@@ -133,7 +133,7 @@ static string cleanRunwayNo(const string& aRwyNo)
   }
 
   string result(aRwyNo);
-  // canonicalise runway ident
+  // canonicalise runway ident to two digits and one optional uppercase letter
   if ((aRwyNo.size() == 1) || !isdigit(aRwyNo[1])) {
     result = "0" + aRwyNo;
   }