Changed password hash and salt according to https://crackstation.net/hashing-security.htm
That is: users' password are salted and then hashed with sha256. Each user has it's own random salt.

Every time a user update her pass or do a login, the password is upgraded too.

WARNING:
    before updating, execute:
      alter table users modify user_pass char(128) not null;
    in the database






git-svn-id: file:///home/gallir/meneame/svn/src@4044 cbe1a1ec-7179-4919-8e32-4551e8279a00