Patch for fixing pb when users have a valid ticket and the server change its password

[Matthieu Patou]

Hello,

Find attach a patch proposal for bug 7099.

My patch store a copy of the previous password on password change and 
try this password for validating tickets presented by the user to the 
server.

This should hopefully solve the bug that when the password of a samba 3 
server is changed: for all tickets that are still valid for the server's 
principals but emitted before the server has changed its password, the 
server is not anymore able to validate them (as it didn't has the 
previous passwords).

I also attached a backport for samba3.5.x (I applied it to 3.5.3 and 
3.5.2 and compiled it on 3.5.2).

Cheers.

Matthieu.

-- 
Matthieu Patou
Samba Team        http://samba.org