GCC has some optimization for the inclusion guard, but they only work if
the check is the outermost one.
We're fairly inconsistent because of historical reasons, so we should
ensure that we follow the same pattern in every public header.
CLUTTER_BIND_POSITION and CLUTTER_BIND_SIZE are two convenience
enumeration values for binding x and y, and width and height
respectively, using a single ClutterBindConstraint.
Instead of using the fixed position and size API, use the newly added
update_allocation() virtual function in ClutterConstraint to change the
allocation of a ClutterActor. This allows using constraints inside
layout managers, and also allows Constraints to react to changes in the
size of an actor without causing relayout cycles.
http://bugzilla.clutter-project.org/show_bug.cgi?id=2319
Allow using the BindConstraint to bind width and height of a source
actor.
Also, add a test for the BindConstraint showing all types of usages
for this constraint class.
