Problem: need UUID construction from string

Solution: add zuuid_set_method.
Problem: not working properly on ZeroMQ/2.x any more

The problems are mainly with inproc bind/connect. In 2.x these have
to come in the right order, and with multiple threads, we need a
short pause before connect is safe to go.

I might fix this in zsock_connect by pause/looping a few times, if
we're on 2.x and the connect fails.
Problem: zsock_connect on inproc is fragile prior to ZMQ v4.x

Historical versions of ZeroMQ did not allow connect-before-bind
on inproc://. This hits especially with multiple threads where
you cannot be sure what order threads start up.

Solution: on ZMQ v2.x and v3.x, if zsock_connect fails with an
ECONNREFUSED error, sleep for 250 msec and then retry. We do this
four times for up to 1 second wait.
Merge pull request #567 from hintjens/master

Fixing CZMQ to work again on ZeroMQ 2.x