Kgio 2.6.0 - kinder, gentler I/O for Ruby!

kgio provides non-blocking I/O methods for Ruby without raising
exceptions on EAGAIN and EINPROGRESS. It is intended for use with the
Unicorn and Rainbows! Rack servers, but may be used by other
applications (that run on Unix-like platforms).

Changes:

minor feature update and cleanups

We now export SOCK_NONBLOCK, SOCK_CLOEXEC constants in the Kgio
namespace to make kgio_tryaccept/kgio_accept easier-to-use.
There are also some minor internal cleanups.