Multiple instances collide in the worker

[Uplink03]

The Pixastic instances share the worker, so if you have two instances that you operate simultaneously the result is not what you want.

The easiest fix is to move var worker; from the shared Pixastic variable space to the constructor so each instance has its own worker:

diff --git a/pixastic.js b/pixastic.js
index c9fb188..e0a7f3f 100644
--- a/pixastic.js
+++ b/pixastic.js
@@ -11,8 +11,6 @@

  var Pixastic = (function() {

-    var worker;
-
     function createImageData(ctx, width, height) {
         if (ctx.createImageData) {
             return ctx.createImageData(width, height);
@@ -22,6 +20,8 @@
     }

     function Pixastic(ctx, workerControlPath) {
+        var worker;
+

         var P = {},
             width = ctx.canvas.width, 

There is probably a better way to do this, but I didn't spend time figuring it out.