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.

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

A stringlist implementation (previously ``private'' to libc netgroup code,
but christos ok-ed making public as it's useful)

argument: 0 (which is not a valid SLC code -- valid SLC codes are currently
1 -> 30 inclusive, from RFC-1184).

install -> ${INSTALL}, -c -> ${COPY}

it is not fully compliant

Correct _POSIX_ARG_MAX; it should define the minimum allowed argument size,
not the supported on (we have sysconf for that)