zmq::socket_poller_t::wait() had an important set of common lines
between POLL and SELECT variant.

Solution: refactor zmq::socket_poller_t::wait() and add the
following methods:

zmq::socket_poller_t::zero_trail_events()
zmq::socket_poller_t::check_events()
zmq::socket_poller_t::adjust_timeout()
Signed-off-by: Marc Sune <mardevel@gmail.com>