Password spontaneous reinitialization

Created by: dverdin

Fixing issue #167 (closed) along with problem reported on the list by Pat Allen: password was reset when subscribing to a list. When updating a user, password was systematically rehashed even if it was not a new password. Consequently, anytime a user was updated, the password was replaced by its own hash. Fixed by checking the database for a pre-existing password before computing the hash. If the hash in database and the value password present in the user data during update are the same, the password is not rehashed.