check rc in monitored queue
catch ETERM in Devices

allows clean exit by terminating the context
Merge pull request #407 from minrk/mq-check-rc

check rc in monitored queue

errors in the inner loop were silenced

also catch ETERM in Devices, allowing clean shutdown of a device without error messages.
add constants from libzmq-3.3.0
updateconstants workaround for ZMQ_NULL
update constants
strip null-termination from bytes-sockopts

excluding IDENTITY
utf16 test fix
use numpy.isnan

to make sure no nan
update int sockopt test exclusions
rebuild constants.c when constants.pxi is updated
test libzmq security