work around "obj in SchemaListProperty" bug
work around "obj in SchemaListProperty" bug

checking "obj in SchemaListProperty" (where SchemaListProperty refers to an
instance of the SchemaListProperty from couchdbkit) does not always
work. workaround by converting to a list first.

gpodder/mygpo,gpodder/mygpo,gpodder/mygpo,gpodder/mygpo