only let user select 'available' workflow items

wcs/admin/workflows.ptl

@@ -193,7 +193,7 @@ class WorkflowStatusPage(Directory):
 
     def get_new_item_form [html] (self):
         form = Form(enctype='multipart/form-data', action = 'newitem')
-        options = [(x.key, _(x.description)) for x in item_classes]
+        options = [(x.key, _(x.description)) for x in item_classes if x.is_available()]
         options.sort(cmp=lambda a, b: cmp(a[1],b[1]))
         form.add(SingleSelectWidget, 'type', title = _('Type'),
                 required=True, options = options)

wcs/workflows.py

@@ -334,6 +334,10 @@ class WorkflowStatusItem:
         pass
     init = classmethod(init)
 
+    def is_available(cls):
+        return True
+    is_available = classmethod(is_available)
+
     def render_as_line(self):
         return _(self.description)