use ROUTER/DEALER socket names instead of XREP/XREQ This is principally a big find/replace, but also adjusts the import-check for pyzmq/zmq versions in IPython.zmq and IPython.parallel. XREP/XREQ are aliases for ROUTER/DEALER in 0MQ 2.x. These sockets continue to exist in 3.0 under the ROUTER/DEALER name only. The XREP/XREQ protocols change some in 3.0, and won't work properly with current IPython. It is likely that once 3.0 is stable (and pyzmq supports it better), we will want to move some sockets back to the *new* XREP/XREQ, but this PR should make IPython safe through libzmq-3.x.