Resolve return value and timeout for multi-command and continuation prompts in replwrap

* for multiple commands, such as in
  ``'\n'.join((cmd, cmd2))``, cmd2 and beyond
  previously used a ``timeout`` of 1, instead of
  the specified or default ``timeout``.
* furthermore, the output of multi-command output
  was discarded, only the last-most command output
  was received.  Resolved by joining the result of
  ``self.child.before``.
I think `res` should be stored as a list, and then we should return `u''.join(res + [self.child.before])`. That's supposed to be more efficient in general than building a string by adding parts on to it.