Only one authentication mechanism is active

[s-edwards]

The authentication config for accounts appears to use local database authentication now (via devise), and LDAP authentication for VT user names is no longer active. Unfortunately, some VT users may have "created" brand new accounts as a result, that are completely separate from any VT-LDAP-based account they had before. We need to track this down and fix the problem, and figure out whether one authentication mechanism (or many, living side-by-side) is best, and make it work that way.