add rm -f to mk()

pcvt days and no longer required

Cleanup so all Quantum disks are now Capitalized.

This fixes namespace problems where STRIP is sometimes used as
the name of the strip(1) to use and other times used as
the flag to send install(1) when stripping (or not).
COPY doesn't have this problem (yet) but was poorly named.

an environment variable

It almost is free of expr but will require more work.
PLEASE let me know if this changes anything ASAP!

Same change doen for SKEY, YP, and KERBEROS5.  This allows
people to override those setting in /etc/mk.conf.

add ~ftp/{motd,spwd.db,pwd.db} mode 0444

necessary to access cdrom and other devices (currently show up as disks)

This is really paranoid, but who knows what some weirdos are capable of?