I planned to use them to simplify wsat_le, but it did not turn out to be simpler.

This reverts commit 5161e463.

Since ssr ad273277 the Global Set Bullet Behavior in modures.base
should do the job.

For consistency, let's deal with autosubst in the same way as with
ssreflect. The user should install it somewhere itself.

This should be documented and possibly discussed later.

And use more uniform variable names.

scons: also compile the barrier/ files. Finding autosubst fails though, since _CoqProject is not used.

The proofs are neither short nor nice, but at least they compile
fast (4 sec for the whole file) and the statements look like
they would look like on paper.