fix RQLUniqueConstraint behaviour by using a DISTINCT query and allowing to specify variables that should be used in selection. See usage on state_of / transition_of relations.

don't fail on error while render a notification mail

improve error message for redundant initial workflow states

fix name error while debugging

oops, this is an object relation

don't use html/dtd validator as default validator for non html views. Closes #550162

support x.set_relations(a_relation=None) to delete a_relation relations from this entity

properly fail if user has entered wrong connection information for the system database, closes #549136

[forms] deprecate form_render(**kwargs) in favor of render(formvalues=None, rendervalues=None, renderer=None) to fix a pitfall in form_render prototype: there is no way to distinguish between arguments that should be given to build_context from arguments that should be given to the renderer. This was problematic for instance with inlined form where a 'title' argument is given for the renderer, but is also used as default value for field whose name is 'title'...

wfhistory isn't anymore selectable if the entity has no record in its history