transfer arugments for Plugin.finish from view_func (update_listing e.g.)

[fanatid]

Right now if you want set update_listing as True, you need write about the following:

plugin.finish(items=items, update_listing=True)
plugin._end_of_directory = True

This patch allow return dict from view_func and passes this dict to plugin.finish in plugin._dispatch. Also allows return Iterable value, it's passed as items.

[tamland]

I think that's pretty much what I did in #84, except for the dict check..

[jbeluch]

This is interesting. Always wanted a way to be able to pass the plugin.finish() args in a simple response object without having to call plugin.finish() explicitly. Adding this optional extra layer would certainly solve that...