Bug 1991: kqueue causes SSL to hang

Bug 1991: kqueue causes SSL to hang

Compare the code in normal select and epoll v.s. kqueue. The select use a 0
wait time to get out of select wait in order to handle a list of read_pendings.
However, epoll add the read_pending to read and write event monitor. At a first
look, this seems strange as why read pending has anything to do with write. It
became obvious when the write ready event is triggered. During a write ready
event, if read_pending is on, the read callback is called before the write
callback. As the write buffer is unlikely to be full for an extended period, a
write callback is guaranteed in the immediate future for the read_pending
socket by waiting on write.

The patch follows that same logic as epoll and applies it on kqueue.