Add _ChrootRandomAccessFile and ForwardingRandomAccessFile (#159)

`ChrootFile.open`/`ChrootFile.openSync` previously returned the
delegate's `RandomAccessFile` directly.  However, `RandomAccessFile`
has a `path` property (sigh) that exposes the underlying path instead
of the chroot'd path.

Add delegating wrapper classes for `RandomAccessFile` so that we can
override the returned `path`.
5 files changed