Solution: use msleep (SETTLE_TIME) everywhere when waiting for the
connections/sockets to be settled instead of a variety of patterns
and functions to make tests more coherent.
There were numerous small issues with test cases:
- some lacked the right source file header
- some were not portable at all
- some were using internal libzmq APIs (headers)
Solution: fixed and cleaned up.
Set the ZMQ_HEARTBEAT_TIMEOUT to default to the value of
ZMQ_HEARTBEAT_IVL if it's not explicitly set.
Change the units of ZMQ_HEARTBEAT_TTL to milliseconds in the API
and round down to the nearest decisecond so that all the options
are using the same units.
Make the maximum heartbeat TTL match the spec (6553 seconds)
