add UNZIP_NATIVE_CMD which is required by Mk/Uses/zip.mk
import Mk/Uses/dos2unix.mk and Mk/Uses/zip.mk from the master branch
import Mk/*.mk from the master to support stagified ports.

You can import stagified ports from the master branch adding
BSDPORTMK=      ${PORTSDIR}/Mk/bsd-staging.port.mk
to the Makefile.