Evaluates to a list of userids of people who match names.
A person matches if every word in names is an initial
substring of some part of their name. If cnum is non-zero,
matching people must also be a member of conference cnum.
Evaluates to a list of all of the userids registered with Caucus
that begin with the initial substring match.
If match is empty, evaluates to list of all of
the Caucus userids.
(Even on a site with thousands of users, this function evaluates quickly.)