Replacing PHPass with password_compat

Per https://github.com/owncloud/core/issues/10050#issuecomment-51333177

also https://github.com/owncloud/3rdparty/pull/110
In case you still do not see what I mean: You can add "return null;" at the top of checkPassword() and this test will still pass. This is testing the wrong thing / on the wrong layer.