$performer: User who performed the change, false if via autopromotion
$reason: The reason, if any, given by the user performing the change,
false if via autopromotion.
+$oldUGMs: An associative array (group name => UserGroupMembership object) of
+the user's group memberships before the change.
+$newUGMs: An associative array (group name => UserGroupMembership object) of
+the user's current group memberships.
'UserIsBlockedFrom': Check if a user is blocked from a specific page (for
specific block exemptions).