[turba] upgradeprefs maintenance task

[Liam Hoekenga]

How / when does the "upgrade prefs" maintenance task get invoked in Turba 
2.2RCx?

I'm trying to figure out a mysterious situation where people's search 
sources are getting set to what looks like a hash for some sort..

+----------+------------+----------------+----------------------------------+
| pref_uid | pref_scope | pref_name      | pref_value                       |
+----------+------------+----------------+----------------------------------+
| liamr    | imp        | search_sources | 687f9b6c5497ce57fa72a9ecce3412b6 |
+----------+------------+----------------+----------------------------------+

Liam