Almost double firefox tight_png render performance.

When extracting the data URI info, much more efficient in firefox to
iterate and push onto an array, then to generate the whole array at
once using the map function.

Chrome is mostly unaffected by this change (might be slightly better).

vnc.js

@@ -902,11 +902,6 @@ display_tight_png: function() {
         //console.log("   png, RQ.length: " + RQ.length + ", clength[0]: " + clength[0] + ", clength[1]: " + clength[1]);
         RQ.shiftBytes(1 + clength[0]); // shift off ctl + compact length
         img = new Image();
-        /*
-        strdata = RQ.shiftBytes(clength[1]).map(function (num) {
-                return String.fromCharCode(num); } ).join('');
-        img.src = "data:image/" + cmode + "," + escape(strdata);
-        */
         img.src = "data:image/" + cmode + "," +
             RFB.extract_data_uri(RQ.shiftBytes(clength[1]));
         img.onload = (function () {
@@ -922,8 +917,11 @@ display_tight_png: function() {
 },
 
 extract_data_uri : function (arr) {
-    return escape(arr.map(function (num) {
-            return String.fromCharCode(num); } ).join('') );
+    var i, stra = [];
+    for (i=0; i< arr.length; i++) {
+        stra.push(String.fromCharCode(arr[i]));
+    }
+    return escape(stra.join(''));
 },