When passing `binmode: true` to `IO.pipe`, it should behave the same way
as calling `binmode` on each of the file handles. It should set the
file to binmode *and* set the encoding to binary on the file.
Before this commit, passing `binmode: true` to `IO.pipe` would make
`binmode?` return `true`, but the file's encoding would remain the same
as the default encoding. Passing `binmode: true` should make `binmode?`
return `true` *and* set the encoding to binary.
