Fixed interface in dossiers ConstrainTypeDecider.

The default adapter should use `Interface` as adapting interface
for the request. Otherwise overriding the ConstrainTypeDecider
in a customer package, is not possible without inheriting from
`Products.CMFDefault.interfaces.ICMFDefaultSkin` in the customers browserlayer.
Merge pull request #259 from 4teamwork/pg_fix_constrainttype_decider

Fixed interface in dossiers ConstrainTypeDecider.