The AlignConstraint update is using only the width/height of the source,
but it should also take into account the position.
Also, instead of using the ::notify signal, it should follow the
BindConstraint, and switch to the ::allocation-changed signal, since
it's less expensive (one emission instead of four notifications, one for
each property we use).
The scanner has some issues when parsing valid gtk-doc annotations; we
should make its (and, in return, ours) life easier.
We still get warnings for code declared in <programlisting> sections,
unfortunately.
Since constructing AlignConstraint and BindConstraint instances could be
deferred (think ClutterScript) we need to make their :source properties
setters accept NULL. This does not break the constraints because they
need to handle that condition in case they actor to which they are
applied is destroyed and somebody is holding a reference on them anyway.
AlignConstraint is a simple constraint that keeps an actor's position
aligned to the width or height of another actor, multiplied by an
alignment factor.
