Handle "no versions" feature in fileify and tovmsspec.

This is a follow-up to d5e61aaf9d7051b136, where we stopped
escaping semicolons in tovmsspec when they appeared to be the
beginning of a version specification but always escaped them
otherwise.

It turns out there is yet another CRTL feature logical name
(DECC$FILENAME_UNIX_NO_VERSION) that tells us a Unix-format
specification is not allowed to have a version number, so in
that case, always escape the semicolon since it can't be the
start of a version specification.

Also, don't add the version number when fileifying directory
specs if this "no versions" feature is in effect.