Avoid NoMethodError in Adapter shutdown method
Don't need to run WEBrick server in a thread
Call stop from Mongrel interrupt handler

The `shutdown` method isn't actually in scope because of how Mongrel
evaluates the configurator block. I could have passed the method into
the configurator as a proc in the options hash (as dispatcher is) but
this is simple, too.
Exit from sleep in Reel adapter's interrupt handler