import-checker: ensure cffi is always a system module I've had reports that this is not always happening, so whitelist it the way we whitelist other problem cases.

atomictempfile: add context manager support Close the file (moving it in place) on clean context exit, discard when there has been an exception.

atomictempfile: add read to the supported file operations

atomictempfile: remove test ordering These tests are independent and numbering only makes it harder to add more and logically group them.

atomictempfile: use a tempdir to keep the test environment clean Rather than pre-emptively delete a file, execute the test in a dedicated temporary directory that is removed after each test.

test-revset: show how inconsistent the ordering of compound expressions is This adds mostly broken tests that will be fixed by subsequent patches. We generally don't do that, but this patch series would be hard to review without a set of broken tests. Note that some tests pass thanks to the reordering problem in optimize(). For instance, '2:0 & _intlist(0 1 2)' doesn't fail because it is rewritten as '_intlist(0 1 2) & 2:0'.