Always prefer JS ops if we have imageData.

All browsers with Canvas imageData are faster with JS ops instead of
canvas ops. This gives significant performance improvement in Opera.
Except for missing web-socet-js message notifications, Opera 10.60 is
now faster than firefox 3.5.

include/canvas.js

@@ -186,13 +186,8 @@ init: function (id) {
             console.log("Using Canvas getImageData");
             Canvas._imageData = Canvas._imageDataGet;
         }
-        if (Util.Engine.webkit || Util.Engine.gecko) {
         console.log("Prefering javascript operations");
         Canvas.prefer_js = true;
-        } else {
-            console.log("Prefering Canvas operations");
-            Canvas.prefer_js = false;
-        }
         Canvas._rgbxImage = Canvas._rgbxImageData;
         Canvas._cmapImage = Canvas._cmapImageData;
     } else {