Make compatible with jQuery. Slight API change.

Rename the $() selector to $D() so that it doesn't collide with
the jQuery name.

The API change is that the 'target' option for Canvas and RFB objects
must now be a DOM Canvas element. A string is no longer accepted
because this requires that a DOM lookup is done and the Canvas and RFB
should have no UI code in them. Modularity.

tests/base64.html

@@ -19,7 +19,7 @@
 <script> 
     function debug(str) {
         console.log(str);
-        cell = $('debug');
+        cell = $D('debug');
         cell.innerHTML += str + "\n";
         cell.scrollTop = cell.scrollHeight;
     }