Ensure the width of widgets is an integer

Particularly the image widget, since I'm derp. Returning floats breaks
other thigns subtly, like the systray widget. This fixes the image
widget, and also prevents other widgets from doing the same mistake.
Fix up gentoo documentation
Whoops... should've bumped this for 0.6
open 1st window after closing win in treeLayout

Closes #355
Closes #356
Don't crash on exceptions from hooks