removing MRI 1.8 support

[Eric Wong <normalperson@yhbt.net>]

Anybody really care for it?

I think it's too painful to support completely due to the way
SPLICE_F_NONBLOCK is handled for pipes and how the file O_NONBLOCK flag
of the non-pipe is relied on.

splice() ignores O_NONBLOCK on the pipe, instead relying on
SPLICE_F_NONBLOCK being passed to it.  However, SPLICE_F_NONBLOCK
only affects pipes, so if you splice a pipe to a socket, you need
O_NONBLOCK on the socket.

Since MRI 1.8 uses non-blocking I/O and select() to schedule
threads, this is painful to deal with for users that may want
to see :EAGAIN or Errno::EAGAIN in some cases and not others.


Hopefully the above explaination is halfway coherent, I really
don't care enough about MRI 1.8 to do a better explanation :<

It may incidentally work in some/most cases, but 1.8 really isn't
worth my effort to maintain...

-- 
Eric Wong