BSD accept() filters
server.bsd-accept-filter = "" (default)
server.bsd-accept-filter = "httpready"
server.bsd-accept-filter = "dataready"
Note: this is a behavior change from prior versions.
The default is now no additional accept() filter, whereas prior
versions unconditionally enabled "httpready" accept() filter
Additionally, server.defer-accept (Linux) is inherited from global scope
into $SERVER["socket"] blocks
github: closes #65