api: make dq socket unique per-handle

Ensure that each handle has unique inproc:// socket names for
its dq sockets.  I don't think this is actually a problem right
now since each API handle currently has its own zctx, but this makes
the code less fragile should we we later allow the zctx to be provided
externally, and shared between handles.
tkvswatch: add a test for issue #85
modules: use inproc sockets for deferred req

    This allows deferred messages to make the reactor ready and
    should address issue #81 for module handles.