Subscribe recorders to proxies

A sketch of a fix for #652 

I'm not sure using `playback` and then sending the message is even sensible, what do people think?

Also: there was a failing spec for me locally, but it was present before this commit. It's  `rspec ./spec/rspec/mocks/partial_double_spec.rb:140 # Using a partial mock on a proxy object works properly`

This is based on top of Myron's branch in: #651