The frame-rpc module is a proper CommonJS module and it's footprint
is really tiny. Its protocol is simpler. It doesn't handle connection
and buffering, but with our onConnect callback we don't need buffering.
The connection handshake that jschannel did was so trivial it's been
re-implemented here (each side tries to connect to the other once).

We have to handle timeouts ourselves, but that's all hidden in the
bridge code. In exchange, we get a simpler API, we get rid of the
call/notify distinction in favor of just passing a callback or not
and we avoid the excess overhead of the recursion guard in the
serialization code that was giving us false positive issues with
the document title.

This is one step toward removing all the browserify-shim requiring
libraries from the injected bundle, which will eventually fix #2397.