Got new test cases working with libzmq

* disabled the specific tests that do not work (yet) on libzmq
* cleaned up one source (test_spec_rep.c) but the others need similar work
* added sleep in test_spec_rep to allow connects time to happen; this would
  not be needed if we connected out to the REP peers instead in from them,
  but I didn't want to change the logic of the test code.
Merge pull request #610 from hintjens/master

Problem: new spec test cases don't all work