(merge from 3.0)

(merge from 3.0)

Revise our server-side password change code to cope with the various
different feilds that different clients send.  (For example, not all clients
send both password types).

This also cleans up the code to make it clearer what is really going on,
and to make better use of common functions.

Andrew Bartlett
(This used to be commit e5b5cd5966f2894c283383abe5d99fda524cbb9f)