Ruby io_splice 2.0.0

Ruby io_splice 2.0.0

There is a new IO::Splice.copy_stream method which is similar to
the IO.copy_stream method in 1.9 core, but uses splice()
internally to avoid copies to userspace in situations where
sendfile() is not possible.

With Linux 2.6.35 (and header files to match), we will also
export the F_GETPIPE_SZ and and F_SETPIPE_SZ constants so
they can be used with fcntl() to resize pipe buffers.

The documentation is also updated to reflect the returned
usefulness of the IO::Splice::F_MOVE constant for FUSE
filesystems under Linux 2.6.35.

I've also relicensed to LGPLv2.1+ (from LGPLv3-only) to allow
bundling with GPLv2-only applications (I'm currently the sole
copyright holder).

Signed-off-by: Eric Wong <normalperson@yhbt.net>