Going to attempt this this week, so as to finish up DM-6625.

Based on chatting with Russell Owen, I'm going to implement getLocalEarthRotationAngle as the "getLST" equivalent (and document it as such) and getBoresightHourAngle(), that uses it. I will use the LST value from the headers to compute an approximate ERA and store that, while making clear in the docs that it is not the "correct" ERA, until DM-8053 is finished.

Please take a look, Russell: I think I got everything, but obs_sdss doesn't have its own makeVisitInfo(), and I wasn't sure what to do about obs_test.

Open questions:

1. is it ok that we're faking ERA (and by extension LST and HA) in this manner?
2. Should I have better tests for afw::getBoresightHourAngle(), afw::getLocalEra() and particularly obs_base.eraFromLstAndLongitude()?
3. Is the approximate calculation I'm using for lsstSim good enough? It doesn't include refraction correction, but it should be relatively close given that we don't want to do the UT1 calculation.
4. Should I manually rewrap LST, HA, and ERA, or leave that to the users (e.g. ERA is not wrapped on output in VisitInfo::write: is it expected to be wrapped when set)?
5. Did I miss any obs packages or aspects of the obs packages I got?

Thanks.

A few minor requested changes to obs_base, but otherwise this looks good.

The lsstSim code is a bit more worrisome only because some of the lsstSim header data is not self-consistent. I'm not sure what to do about it, but I worry that folks will trust info that is dead wrong.

To deal with lsstSim's inconsistencies, I've clarified with a comment and then explicitly test for ERA==NaN. That's the best we can do for now: I'll just have to work around it in jointcal.

Everything is merged (including one "reverse rebase" of obs_base that appears to be fine...), and I cleaned up one bad rebase that Colin Slater noticed. Just to be sure nothing to got mangled, I've done two final Jenkins runs of the current master:

https://ci.lsst.codes/job/stack-os-matrix/18316/ (full demo)
https://ci.lsst.codes/job/stack-os-matrix/18321/ (py2/3 lsst_py3)