This adds new 'over' and 'under' transitions which work by moving
the new page over the previous one, or moving the previous page off
to reveal the new one. We also add an over/under combination that
is going to be used in GtkAboutDialog.
https://bugzilla.gnome.org/show_bug.cgi?id=707187
The child property is watched by the StackSwicther which in turns sets a
needs-attention css class on the corresponding button, so that the theme
can for instance show a throbbing animation if one of the hidden pages
needs the user attention.
https://bugzilla.gnome.org/show_bug.cgi?id=707153
Since we now do all drawing propagation on the cairo_t (rather than
exposing multiple independent times on the GdkWindows) we no longer
need the opacity 0.999 hack.
We should only draw the cross-fade on the bin window, not doing this
was causing us to draw it multiple times using ADD which resulted
in weird colors.
Add separate GtkStack and GtkStackSwitcher widgets that are an
alternative to GtkNotebook. Additionally, GtkStack supports
animated transitions when changing pages.
These widgets were initially developed in libgd.