rebase: create a new variable to make the next patch more legible

rebase: minor refactoring of _computeobsoletenotrebased This patch is a refactoring of the code skipping obsolete changesets already present in destination. It makes the following patches more legible. Instead of passing all the revs to be rebased to _computeobsoletenotrebased, we only pass the obsolete revisions of the rebaseset.

test-status: stabilize for no-execbit platforms The preceding #if conditional was the only modification to the file, so the "reverting file" line in the subsequent revert command was getting dropped.

merge: split up checks for unknown and ignored files that differ In some real-world cases it is preferable to allow overwriting ignored files while continuing to abort on unknown files. This primarily happens when we're replacing build artifacts (which are ignored) with checked in files, but continuing to abort on differing files that aren't ignored. We're redefining merge.checkunknown to only control the behavior for files that aren't ignored. That's fine because this config was only very recently introduced and has not made its way into any Mercurial releases yet.

merge: determine what untracked conflicts cause warns and aborts separately This is written in a somewhat weird style, but it's designed for code reuse in an upcoming patch.

merge: factor out code to get checkunknown config We're going to reuse this code shortly.