This allows other programs to link in against ls (e.g, ftpd), without having
to have hacks to deal with multiple main()s.
Yes, I know this is ugly. The clean alternative (move lots of this
into libutil, yada yada yada) isn't fun, and the effort probably isn't
justified...
* in printcol(), don't bother building an index to the linked list if
only printing one column with printscol()...
* implement -n; prevent [gu]id->name mapping in long listings.
inspired by openbsd, but does *not* imply -l by itself.
* fix sorting with -d (or mismatched types in general). (from openbsd).
* document -g. (from openbsd).
lukem