net.cqueues previously relied on timers instead of fd events sometimes.
Under net.server_select, it would have called cq:loop() on every
iteration of the main loop, which was probably not optimal.
Why? Just look at all that code deleted!
watchfd is the prefered way to poll things that expose FDs for this
purpose, altho it was added after net.cqueues.
This was originally put in place as a fix for what ended up a cqueues bug: https://github.com/wahern/cqueues/issues/40
A check for a cqueues version with the bug fix is included.
