StThemeNodes may have properties - namely shadows - which paint
outside an actor's allocation. This is not a problem unless drawing
is redirected to an offscreen buffer, in which case the actually
painted size is needed in advance when setting up the buffer.
Add a convenience method to calculate an allocation large enough to
paint the node.
https://bugzilla.gnome.org/show_bug.cgi?id=619025
The (optional) spread radius allows to make the shadow bigger without
enlarging the blur value. Mozilla supports this parameter for the
-moz-box-shadow property.
https://bugzilla.gnome.org/show_bug.cgi?id=613832
Add support for a new -st-shadow property, which is based loosely
on the CSS3 box-shadow property:
http://www.css3.info/preview/box-shadow/
It defers from the specification as follows:
* no multiple shadows
* the optional color argument may be placed anywhere
* the shape is not determined by the widget's bounding box,
but by the background-image property
https://bugzilla.gnome.org/show_bug.cgi?id=603691