The attached patch enables keeping the plaintext
password in the Password class in roundup/password.py
-- in both, the constructor, and the setPassword method.

The benefit: Keeping the plain pw makes it accessible
in detectors. This enables us to
- make checks on the strength of the pw
- generate other pws like, e.g. NT password hash or Lan 
  manager passwords for which we need cleartext.

Security consideration:
Since python does garbage collection there is no
guarantee that a parameter passed to the constructor
will be overwritten anytime soon, so there is probably
no added insecurity keeping the password. Since python
strings are immutable, we can't find a solution that
would securely wipe the given password anyway.

When we're at it, we might go one step further and
refactor the class to call setPassword from the
constructor, so that pw computation is only in one
place. This has the added benefit that we honor the
scheme given in the constructor for new passwords --
currently a scheme given in the constructor is ignored
and the created pw is always forced to scheme =
default_scheme. This would also fulfill the promise
made in the constructor docstring: "Call setPassword if
plaintext is not None." Also setPassword does currently
not set self.scheme, this is also fixed.

- See two patches attached, patch-pw-simple and
patch-pw-refactor.

Ralf