Retry on EINTR error

For whatever reason ZMQ now raises ZMQErrors with an errno.EINTR code.
We simply retry when they occur.

fixes #62
Fix a broken unit test

For who is intersted by the resolution:
 - a channel cannot be considered opened until the endpoint answered
 - the code was sending 2 events in a row...
 - the first event will open the channel
 - but if the second event arrive "too fast", the channel wont be "fully
   opened"

The solution:
 - wrap the channel in a BufferedChannel, which automatically prevent
   sending more than one message until the channel is opened fully.
bump version to v0.4.2
EINTR, EINTR eveywhere!

for some reason, zmq thorw EINTR on getsockopt calls now...
ref #62
bump version to v0.4.3
the latest zerorpc code needs at least pyzmq 13
Merge pull request #64 from jpetazzo/fix-pyzmq-dependency

the latest zerorpc code needs at least pyzmq 13
fix tests

event args were expected to be tuples, but they are lists
use logging instead of printing to stderr