100996 – bsd.port.mk: add macro to copy with right permissions directory trees

no flags

        We have a lot of ports (thousands, actually), that need
        to copy entire directory trees to specific location,
        e.g. when installing examples for port one could issue:

        @${TAR} -cf - -C ${WRKSRC} copyfs cryptfs gzipfs uuencodefs tests | \
                       ${TAR} -xf - -C ${EXAMPLESDIR}
        @${FIND} ${EXAMPLESDIR} -type f -exec ${CHMOD} ${SHAREMODE} {} \;
        @${FIND} ${EXAMPLESDIR} -exec ${CHOWN} ${SHAREOWN} {} \;

        There are many other solutions (e.g. using PAX, FIND, CPIO combinations)
        , buth every require one important step - set up permissions for
        installed files, since this files are not processed by INSTALL_XXX
        program.

        A lot of ports usually forget to do this - I began to fix some
        of them - but it's tedios and giant work...

        The macros introduced allows to dial with such tree ierarchies
        in handy and efficient way. For previos example one can use:

        cd ${WRKSRC} && ${COPYTREE_SHARE} "copyfs cryptfs gzipfs uuencodefs test
        s" "${EXAMPLESDIR}"

        and that's all.

        I decided to use CPIO (though I don't like it)  since it can be used
        with find program, that allows to manipulate on file sets with a great
        power. Additional commands to FIND program might be passed by third
        argument to macro, e.g. to eclude 'Makefile" file we can use:
        cd ${WRKSRC} && ${COPYTREE_BIN} docs "${DOCSDIR}" "! -name Makefile"
	
        Thus, this macro allows to use the whole power of FIND program.

	Also, I've used "-l" swith in CPIO to speed-up copies in some
	cases. That's why I've redirected cpio output to /dev/null ;-)

        It would be nice to have you comments/suggestions here. Thanks!