rebase: improve invalid revisions filtering - Filter rebasestate nullmerge and unrebased revision before considering updating obsolete. This simplifies the handling of obsolete and make it ignore unrebased revision rather than extinguishing them. - Apply obsolete markers only if rebasestate is not empty, testing rebasetarget was irrelevant.

all: tutorial
	sphinx-build . ../html/

tutorial:
	python test2rst.py tutorials/