Doug's fix for my MAILGROUP autoconf support on his platform (yep, I was

Doug's fix for my MAILGROUP autoconf support on his platform (yep, I was
ignorant about that "wheel" group) broke it on my platforms (AIX 4.1.5.0.01 and
Solaris 2.6).  `ls -lg` doesn't do what Doug was expecting on these platforms --
it displays _only_ the group rather than the user and the group (thus awk
'{print $4}' did the wrong thing).

Also did some miscellaneous cleanup, like making variables that were intended to
be cached actually be cached (renamed to nmh_cv_*, etc.), and using the $AWK
that we've auto-detected rather than relying on the $PATH to find one.