[Owncloud] Review of pull request#26(improved persistent cookies) - second pair of eyes required

[Michael Göhler]

Hi together,

don't be surprised, im currently sick and at home ;)

I took Bart's approach and added everything I suggested in #26. Can you
please review again before I create the merge request?

https://github.com/visit1985/core/compare/persistentcookies

- I've removed the backwards compatibility to the old token entries in
  preferences table, because this would result in to many extra code
  when checking/deleting them.

- We have to add a password box to the email address field in personal
  settings, because an attacker kann reset the password if we don't!
  I'll have a look on that too, but in another merge request.

Thanks,
Michael