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.

6c6bb7a23bb5125bf06da73265f039dd3447dafa 0.1.0
d3f20770b86a31dba56ae7b252089e12b34702da 0.2.0