Plugin class loading

[Rick McGuire]

While working on my iiop plugin to enable Yoko for Geronimo, I noticed 
that the PluginManager is using Class.forName() to load the plugin 
implementation.  For my iiop plugin at least, the dynamic loading is 
going to require using the current context class loader to load the 
class rather than using Class.forName().  A quick search reveals that 
Class.forName() is used 23 places in the Yoko code.  I suspect many of 
these should be changed to use the context loader as well.  I'm willing 
to make these changes if we agree that's the proper way to do the loading.

Rick