upgrade: explicitly warn when a `--no-xxx` flag is overwritten
Some format upgrade/downgrades -needs- revlog to be recomputed. So we now
detect that individually and warn when it contradict explicitly passed flag.
This is part of a larger series to make `debugupgraderepo` smarter about which
revlog it picks by default.
Differential Revision: https://phab.mercurial-scm.org/D11869
Set up
$ hg init repo
$ cd repo
Try to import an empty patch
$ hg import --no-commit - <<EOF
> EOF
applying patch from stdin
abort: stdin: no diffs found
[10]
No dirstate backups are left behind
$ ls .hg/dirstate* | sort
.hg/dirstate