merge with stable

graphmod: safer code when a changeset has two identical parents While this situation should never under normal use, some real life repos sometimes contain such changesets (older hg versions, broken rebases, etc...) hgweb was displaying an "Internal error" in this case, and graphlog displayed a redundant branch all the way to null: it does not cost us much to just ignore this extra parent when constructing the DAG.

revlog: fix descendants() if nullrev is in revs We were not returning the correct result if nullrev was in revs, as we are checking parent(currentrev) != nullrev before yielding currentrev test-convert-hg-startrev was wrong: if we start converting from rev -1 and onwards, all the descendants of -1 (full repo) should be converted.