The script overwrites document.write in order to serialize all rendering

The script overwrites document.write in order to serialize all rendering

The first version of openx.js had sometimes freezed the IE 8. The cause of
this probably was a race-condition while moving the nodes with the banner
to their final destination.

Because of that, the script serializes all modifications of the DOM
strictly now. Implementation-Details:
 * The HTML delivered by OpenX is parsed, in order to detect included
   script-tags.
 * HTML-code is written to the destination-node directly.
 * script-tags, that load additional code are loaded via a script-node,
   that is appended to the end of the page. The script waits, until the
   additional code is loaded, by adding an onload-event to the appended
   script-node.
 * script-tags with inline-code are executed directly via eval().
 * Calls to document.write() in the additional scripts are catched. To
   achieve that, openx.js overwrites document.write with its own
   implementation, that simply adds the code to an execution-queue, that
   is processed, when the onload-event fires or when the eval()-call
   returns.

TODO:
 * Not tested with IE!