Don't save Curve._hooke when pickling or deepcopying.

Don't save Curve._hooke when pickling or deepcopying.

Two reasons:
1) It crashes because hooke.config._comment_textwrap contains a
   compiled regexp, and these cannot be deepcopied.  See
     http://mail.python.org/pipermail/python-dev/2008-November/083348.html
     http://bugs.python.org/issue416670
2) We don't want to copy Hooke instances anyway, since we need them to stay
   in sync.  Anything copying curves (e.g. Playlist.filter) should shallow
   copy Hooke instances between the curves.
If this turns up anywhere else, we should think about adding a
Curve.copy method to get the "just right" copy depth ;).