etiquette for new failing test cases, followed by fix

I have found a serious bug in reqmuo(3), and a fix in FreeBSD, validated
by regression tests in proj and a hand-written test.  The problem exists
in current and 10, and surely in 9 but I haven't checked.

We currently have no remquo test.  I've written one, stealing from
tests/lib/libm/t_sin, and it shows some failing output.

I'm about to (assuming each step is ok)

  - do a build and then anita run of current with my new test, and
    without the fix

  - commit the test

  - apply the FreeBSD fix locally, and build/anita

  - commit the FreeBSD fix

  - apply a further fix locally, and build/anita

  - commit that

  - request pullups of the test and fix to 10

  - probably not request pullups to 9, unless someone asks for them,
    since 9 is crufty and really everyone on 9 should be upgrading.

  - consider remquof and remquol after all this settles

Is this reasonable?  It will show an increased failing test for a bit,
but the test really does fail, and my impression is that the xfail
scheme is about keeping known-failing not-getting-fixed tests from
obscuring "we just had a regression", which a few days of this won't do.

(Absent objections, I'll proceed as above.)