TODO
----

Implement button selection support, where a regular expression can be
applied to button titles for selection.  Test if it is possible to
drag this entire selection, else compile the titles into a string for passing.
Drag and drop of any selected widget should perform this compilation.
Any unselected widget dragged when others are selected should unset the
selection, though this may be reconsidered, as it is useful to have a selection
preserved when doing other operations--keep selection until it is explicitly
changed.

Add gnome session management support.  

