Removing libpng from ext and removed the libpng build command from the ext build target. Added the -DPNG_SKIP_SETJMP_CHECK flag to the linux2-config.py build config file. This should allow users to use their local copy of libpng rather than relying on the libpng in ext. Users should probably clean out their <fife>/etc/install/* directories and re-run 'scons ext'. Tested on ubuntu 10.04

libguichanincludedir = $(includedir)/guichan/widgets/

libguichaninclude_HEADERS =	\
	button.hpp		\
	checkbox.hpp		\
	container.hpp		\
	dropdown.hpp		\
	icon.hpp		\
	imagebutton.hpp		\
	label.hpp		\
	listbox.hpp		\
	scrollarea.hpp		\
	slider.hpp		\
	radiobutton.hpp		\
	tab.hpp			\
	tabbedarea.hpp		\
	textbox.hpp		\
	textfield.hpp		\
	window.hpp