StWidget reports a paint volume large enough to paint the current
theme node. As CSS transitions also paint the previous theme node,
the reported paint volume may be incorrect, resulting in screen
artifacts when painting outside the reported volume.
Add st_theme_node_transition_get_paint_box() to calculate an allocation
large enough to paint both theme nodes, and use it to report the correct
paint volume during transitions.
https://bugzilla.gnome.org/show_bug.cgi?id=640085
* Make sure all source files have a LGPL copyright header, and standardize
non-standard variations of the header to a common form.
* Check and update all copyright notices.
* Remove 'Written By:' lines. They are universally incomplete and
typically indicate only who started a particular file.
https://bugzilla.gnome.org/show_bug.cgi?id=634550
