sylvain.thenault@logilab.fr [Thu, 12 Mar 2009 19:39:34 +0100] rev 1101
unification of meta-attributes handling:
* remove has_format, has_text_encoding, format, text_encoding methods on Entity
* remove rich_text_fields method on EntitySchema
* use instead has_metadata / meta_attribute on EntitySchema (from yams)
and attribute_metadata on Entity