The broken non-seeking read implementation of ResourceFile is removed,
and non-seekable streams are now handled by reading the entire stream
data first and wrapping it in a BytesIO to make it seekable.
The manual selection of seeking/non-seeking reading has been removed as
well, since it is no longer needed and was already nearly useless.
When using ResourceFork.open, the stream is still closed when the
ResourceFile is closed, because the user has no access to the stream.
This matches the behavior of modules like zipfile and tarfile, which
close their underlying streams if they created them themselves, but not
if they were supplied by the user.
