install libzmq on travis
reorder system/bundled libzmq on travis

(faster one goes first)
try testing pypy on travis
fix exclusion of pypy+ZMQ=bundled
allow pypy to fail
can't trust travis Cython

it's too old
minor travis pip tweak
Merge pull request #358 from minrk/traviszmq

some travis tweaks

- fix non-bundled zeromq
- start testing pypy, even though it doesn't work, and won't until travis starts shipping 2.0.