setjmp for the png error handler. It seems setting the error handling

setjmp for the png error handler. It seems setting the error handling

2000-06-09  Larry Ewing  <lewing@helixcode.com>

	* gdk-pixbuf/io-png.c (gdk_pixbuf__png_image_load_increment):
	setjmp for the png error handler.  It seems setting the error
	handling functions does not avoid the jump, and so not calling
	setjmp was causing the incremental loader to jump into lala land.
	(gdk_pixbuf__png_image_begin_load): setjmp for error handling, I'm
	not sure this one is actually required but the docs say it must be
	set for every call to a png_* function.
	Also changed the comment to reflect the fact that setting the
	error handlers does _not_ avoid the longjmp.