add temporary code to dump btree contents on assertion failure described

add temporary code to dump btree contents on assertion failure described

2001-10-22  Havoc Pennington  <hp@redhat.com>

	* gtk/gtktextiter.c (_gtk_text_iter_forward_indexable_segment):
	add temporary code to dump btree contents on assertion failure
	described in #62656

	* gtk/gtktextbtree.c (ensure_end_iter_segment): add some
	assertions that we're getting the right end iter segment

	* gtk/gtktextiter.c (_gtk_text_iter_forward_indexable_segment):
	verify that we aren't on the end iterator after moving
	forward one segment - fixes return value in an obscure case.
	Also, some trivial code cleanup/rearranging.