fix SurfaceArray.blitArray(); change Surface.getImageData() semantics

there is a distinction between ImageData class and the actual image data,
which is contained in that class as property `data`. I confused those.

Browsers accepted the raw data as ImageData but were throwing errors.

lib/gamejs.js

@@ -720,11 +720,11 @@ Surface.prototype.setAlpha = function(alpha) {
  * starting with the top left, with each pixel's red, green, blue, and alpha components
  * being given in that order for each pixel.
  * @see http://dev.w3.org/html5/2dcontext/#canvaspixelarray
- * @returns {Array} the pixel image data (the canvas pixel array in html speak)
+ * @returns {ImageData} an object holding the pixel image data {data, width, height}
  */
 Surface.prototype.getImageData = function() {
    var size = this.getSize();
-   return this.context.getImageData(0, 0, size[0], size[1]).data;
+   return this.context.getImageData(0, 0, size[0], size[1]);
 };
 
 /**

lib/gamejs/mask.js

@@ -15,7 +15,7 @@ var objects = require('./utils/objects');
  */
 exports.fromSurface = function(surface, threshold) {
    threshold = threshold && (255 - threshold) || 255;
-   var imgData = surface.getImageData();
+   var imgData = surface.getImageData().data;
    var dims = surface.getSize();
    var mask = new Mask(dims);
    for (var i=0;i<imgData.length;i += 4) {

lib/gamejs/surfacearray.js

@@ -123,7 +123,8 @@ var SurfaceArray = exports.SurfaceArray = function(surfaceOrDimensions) {
       data = imageData.data;
    } else {
       size = surfaceOrDimensions.getSize();
-      data = imageData = surfaceOrDimensions.getImageData(0, 0, size[0], size[1]);
+      imageData = surfaceOrDimensions.getImageData(0, 0, size[0], size[1]);
+      data = imageData.data;
    }
    return this;
 };