Fix bug 5831 - Clipping problems in summary view draing scrollable
	labels.

	* libnautilus-extensions/Makefile.am:
	* libnautilus-extensions/nautilus-viewport.c:
	(nautilus_viewport_initialize_class),
	(nautilus_viewport_initialize), (nautilus_viewport_draw),
	(nautilus_viewport_paint), (nautilus_viewport_new):
	* libnautilus-extensions/nautilus-viewport.h:
	New files.  A sublcass of GtkViewport that takes into account the
	width and height of the widget style xthickness and ythickness
	when painting.

	* components/services/summary/nautilus-view/nautilus-summary-view.c
	: (generate_summary_form):
	Use NautilusViewport instead of GtkViewport to avoid clipping
	problems when painting labels inside scrollable viewports.