Fix change password dialog for admin users.
Fix change password dialog for admin users.

Fix change password for admin users that have a config entry as well
as a _users doc.

The password change flow is now:

 - if the current user has the _admin role set
   - if it has a corresponding config entry
     - update that entry
 - if the current user has a user doc
   - update that user doc

apache/couchdb-futon,apache/couchdb-futon