Bug 1010 - ClutterLabel does not update the layout (again)

	Bug 1010 - ClutterLabel does not update the layout (again)

	* clutter/clutter-label.c: Bring back layout caching. This time it
	will cache up to three different layouts. The width for which each
	layout was generated is stored so that if the same width is
	requested again it can use the cached version. If no cached
	version is available it will try to replace the oldest
	layout. 'Age' is determined by a counter which is incremented
	every time a layout is created. The cache is cleared after any
	property changes that might affect the layout.
	(struct _ClutterLabelPrivate): Removed extents_width,
	extents_height and context because they weren't used anywhere.

	* tests/test-label-cache.c: Add a test which checks whether the
	label is using a different layout when properties are
	changed. Also compares the extents of the label's layout with an
	independent layout and fails if they aren't the same.

	* tests/Makefile.am (noinst_PROGRAMS): Add test-label-cache