Log Message:
The previous update to the isc-dhcp packages replaced @PREFIX@ and
@PKG_SYSCONFDIR@ with hardcoded paths to /usr/pkg, possibly due to SUBST_STAGE
being set to post-patch.  Revert that change, move SUBST_STAGE to
pre-configure, and perform some minor cleanup while here.

Bump PKGREVISION of all packages, ignoring pkglint's error that this shouldn't
be done in Makefile.common.