kgio 2.4.0 - portability fixes and more

== All supported platforms (*nix + MRI 1.8+, Rubinius)

* OpenBSD (and possibly other *BSD) fixes, thanks to Jeremy Evans.

* kgio_accept and kgio_tryaccept now take an optional second argument
  for flags (like the accept4() flags argument).

== Ruby 1.9-only things

* Kgio.poll no longer raises Errno::EINTR to match IO.select.

== Ruby 1.9 trunk things

* close() on an active FD in a different thread is better
  handled/detected.

* copy-on-write for strings is properly triggered