improvements to generated export string (matches more closely to expected result)

fcore/quad-tree.sml

@@ -501,7 +501,7 @@ struct
   fun intToRealString num =
     let
       val result = Real.fromInt num
-      val result = Real.toString result
+      val result = Real.fmt (StringCvt.FIX (SOME 15)) result
     in
       if String.isSubstring "." result then result else result ^ ".0"
     end
@@ -509,7 +509,7 @@ struct
   fun colToRealString col =
     let
       val result = Real.fromInt col / 255.0
-      val result = Real.toString result
+      val result = Real.fmt (StringCvt.FIX (SOME 15)) result
     in
       if String.isSubstring "." result then result else result ^ ".0"
     end