Apparently, the refactoring to make this script only run when changes
are present was buggy, in that if `apt-get update` failed, running
provision against wouldn't rerun `apt-get update`, resulting in a
broken state that requires expertise to fix. This closes that gap, by
using a stamp file to ensure we always successfully update apt before
proceeding.
It doesn't fix existing installations.
We can't fully support it until we fix the tsearch_extras availability
issue, but for now, this is an improvement.
Tweaked by tabbott to cover the outstanding tsearch_extras issue.
This reverts commit 3f95e567c1.
Apparently `apt-add-repository` fails periodically in CI. I suspect
this is some sort of silly networking problem, but given that all
we're saving is a few lines of code, the old version was better if
this fails basically ever.