Fixed 'unable to cast transparent proxy to type' exception.

Seems to have been caused by the custom appdomain base -- this allows
the new appdomain to load the type, but it fails in the current appdomain.

However, merely adding an AssemblyResolve handler that calls Assembly.Load
seems to fix it. Definitely needs testing on a clean box, though.

Links:

* http://www.west-wind.com/weblog/posts/2009/Jan/19/Assembly-Loading-across-AppDomains