select: Fix -assert-none and -assert-any error output and docs

select: Fix -assert-none and -assert-any error output and docs

Both of these options consider a selection containing only empty modules
as non-empty. This wasn't mentioned in the documentation nor did the
error message when using `select -assert-none` list those empty modules,
which produced a very confusing error message complaining about a
non-empty selection followed by an empty listing of the selection.

This fixes the documentation and changes the `-assert-none` and
`-assert-any` assertion error messages to also output fully selected
modules (this includes selected empty modules).

It doesn't change the messages for `-assert-count` etc. as they don't
count modules.