largefiles: convert addlargefiles() to vfs

rebase: clarify comment about merge ancestor when rebasing merges The code for picking a merge ancestor when rebasing merges had a long and incorrect comment. The comment would perhaps have been fine as commit message but does not make the code more readable or maintainable and is a bad substitute for correct and readable code. The correct essense of the comment is quite trivial: a merge of an ancestor of the rebase destination and an 'outside' revision can be rebased as if it was a linear change, using 'destination ancestor parent' as base and pretty much ignoring the 'outside' revision. The code path where the comment is placed is however also used for other kinds of merge rebases. The comment is thus not really correct and not helpful. I think it would be better to drop the comment and rewrite the code.

status: don't list files as both clean and deleted Tracked files that are deleted should always be reported as such, no matter what their state was in earlier revisions. This is encoded in in two conditions in the loop in basectx._buildstatus() for modified and added files, but the check is missing for clean files. We should check for clean files too, but instead of adding the check in a third place, move it earlier and skip most of the loop body for deleted files.