When performing an incremental reindexing of users, Haystack emits

warnings that it has no way of determining the age of an entry for

users, since there's no sort of "last updated" field available.
We do have a workaround, in that Review Board does update the

last_login field when users access the site, rather than just when

they explicitly log in. We can tie updates to that.
What this basically means is that we will re-index any active accounts

(which might have information changed), but if information is changed

with an older account, it won't be noticed without performing a full

re-index.

Performing an incremental reindexing and saw that the warnings went

away, and the new information on a user was indexed.