No 3.21 yet, but a few fixes in the repository

[Nikodemus Siivola]

I've just merged a couple of fixes to Screamer, in addition to work on
the manual:

* MAXV and MINV work right in the single argument case as well,
restricting it to be real, and returning its value, not the
argument variable.

* (ASSERT! (EQUALV ...)) on things with enumerated domains had
several buglets, some of them causing bogus errors to be signalled
at runtime, some of them causing the system not to realize that
the variable had become bound even though logically there was
enough information.

* WHEN-FAILING is thread-safe. (Previously WHEN-FAILING in one
thread also affected all other threads.)

Cheers,

 -- Nikodemus