Incomplete implementation of $/ = \number acting like read()

Incomplete implementation of $/ = \number acting like read()

It's under tested, and incomplete

- readline appears to ignore IN_BYTES, so this code continues to do so.

- currently :utf8 will return invalid utf8, which means this can too,
  if we can be sure of :utf8 returning only valud utf-8 the FIXME can
  be ignored

- VMS is the elephant in the room - the conditional means that the new
  code is completely ignored for reading from files.  If we can detect
  record-oriented files in some way this could change.