Index names consistently set to "alt" for alternatives files

[dhensle]

Fix for #846.

In addition to CI tests, also successfully ran the SANDAG (cropped) estimation data through estimation mode and confirmed the creation of school escorting and joint tour frequency and composition EDBs.

[jpn--]

This looks fine to me. @dhensle Just one (new) thing to do: please add a section to docs/dev-guide/changes.md about this change, under the Upcoming Changes section at the top.

[dhensle]

@jpn-- I have update the change log for your review. Also, I tried to repair the progressive mtc test by unzipping, changing the Alt column name to alt in the school escorting bundle that was failing, and re-zipped it back up, but now I am getting some weird error about not finding the input checker log. Is there something different you do to create the zip file that maybe I messed up?

[jpn--]

@dhensle Typically when I need to regenerate the progressive tests it's because the numbers have changed slightly, so I just delete the regression targets and re-run, which should automatically regenerate the files. But for a change like this where the numbers are all the same and it's just a header that's changed, what you describe should work -- and I'm surprised it didn't.