widget creation and parent assignment

Team,

The composition of widgets as been done by passing the parent of a
widget to the widget create routine.  This has worked great so far, but
the concerns Marc raised in the beginning are finally rearing their ugly
faces.  Composed widgets (those consisting of more than widget, like
scrollbox, the future combobox, etc.) currently cannot be built
correctly as their is know way to assign the parent of a widget after it
has been constructed.

I propose the following modifications to libstk:

1) we add another create routine for every widget which does not take a
parent pointer.  When using this routine, users are reponsible for
composition, ie they must call my_scrollbox->add(my_widget) on their
own.  Typically users will not use this approach, but it will be nice to
have the option, it will be used by the library in all composite
widgets.

2) add a parent(container::ptr new_parent) routine to widget which
allows for the explicit setting of the parent_ member after
construction.

3) remove the parent pointer assignment from the widget constructors and
move it into the container::add(widget::ptr item) routine.  Whenever it
is called it checks if item has a parent, if so, tell the parent to
remove the item, add the item to itself, and sets the items parent to
itself.

Thoughts / objections / flames?

Darren