newvers.sh has supported a variable setting only mode, use that in
preference to grep to future proof this script from changes there.
Differential Revision: https://reviews.freebsd.org/D19849
Note: tcsh(1) has a MK_TCSH=no test, so this should be a separate
package, which requires pre-install/post-install scripts, to be
added later.
Sponsored by: The FreeBSD Foundation
