[PATCH] accept_nonblock supports "exception: false"
This is analogous to functionality found in IO#read_nonblock and
IO#wait_nonblock. Raising exceptions for common failures on
non-blocking servers is expensive and makes $DEBUG too noisy.
This also increases performance slightly, see patch for benchmarks.
I also intend to support this in the "openssl" extension as well as
supporting connect_nonblock if this is accepted.