extend selection of modes for schema instances

git-svn-id: svn://svn.cy55.de/Zope3/src/cybertools/trunk@3624 fd906abe-77d9-0310-91a1-e0d9ade77398

composer/schema/instance.py

@@ -55,7 +55,7 @@ class Instance(BaseInstance):
                 fi = f.getFieldInstance(self)
                 name = f.name
                 value = getattr(self.context, name) or fi.default
-                if mode == 'view':
+                if mode in ('view', 'preview'):
                     value = fi.display(value)
                 else:
                     value = fi.marshall(value)