Handle alternate null filename for cvs.

'cvs diff' usually uses '/dev/null' for the name of old files, but on Windows
it can return 'nul:'. Check for this as well. Trivial change.

Fixes bug 2294.
Fix an UnboundLocalError.

Christian's change for fixing field_classes typoed fieldset as field_cls.
Trivial fix.
Fix two bad calls to save with update_fields.

The recent improvements to the review request draft save logic resulted
in a bad attempt to pass update_fields. The '=' was missing, resulting
in update_fields being treated like a dictionary, which didn't exist.

This fixes the two calls to properly save with update_fields.