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)