4 different authentication methods in db registration dialog

Michael Hieke
committed code to support 4 different authentication methods in
the database registration dialog:

 - Use saved user name and password
 - Use saved user name and encrypted password
 - Use saved user name, but always ask for password
 - Use trusted user authentication

The method is selected via a choice control.  For the last two the
password entry field is disabled, for the last one both the user name
and the password entry fields are disabled.

Empty password is supported now for the first method.  Unfortunately our
user management does not allow for empty passwords.  Supporting the
creation of users without password is easy (remove two lines from IBPP),
but deleting the password of an existing user is impossible ATM.  This
needs more work anyway.

I had to modify our internal copy of IBPP slightly, will add patches for
that to SF tracker.

Testing and comments very welcome.

please download an 0.9.x snapshot
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