Align phpass to official source code

phpass latest version is 0.4, and the only difference with 0.3 is the same
fix that we did.
Let's align our source code with the official one.

See http://cvsweb.openwall.com/cgi/cvsweb.cgi/projects/phpass/
Merge pull request #1680 from mlocati/official-phpass

Align phpass to official source code