Handle invalid directory spec with EFS in pathify_dirspec.

Handle invalid directory spec with EFS in pathify_dirspec.

When Extended Filename Syntax is enabled on VMS (which is not [yet]
the default), we were allowing invalid directory specifications
consisting of a .DIR extension but some version other than ;1 to
be passed through.

Now we flag that as an invalid directory just as we were doing
without EFS.  This gets a test passing in vms/ext/filespec.t that
was failing under EFS.