Updated some MySQL properties and MigrationHandler stuff

DataSource/MySQL/MySQL.py

 class MySQL(object):
 
     relations_table_name = 'relation'
+    relation_table_pkname = 'id_relation'
     relations_field_nature = 'nature'
     field_lodel_id = 'lodel_id'
     class_table_prefix = 'class_'
     # @param type_name str
     # @param field_name str
     # @return str
-    def get_r2t2table_name(cls, class_name, type_name, field_name):
-        return "%s_%s_%s" % (class_name, type_name, field_name)
+    def get_r2t2table_name(cls, class_name, type_name):
+        return "r2t_%s_%s" % (class_name, type_name)
 
     @classmethod
     ## @brief gets the fk name between two tables

EditorialModel/migrationhandler/mysql.py

     def _r2t2table_name(self, em, emfield):
         emclass = emfield.em_class
         emtype = em.component(emfield.rel_to_type_id)
-        return self.datasource.get_r2t2table_name(emclass.name, emtype.name, emfield.name)
+        return self.datasource.get_r2t2table_name(emclass.name, emtype.name)
         #return "%s_%s_%s"%(emclass.name, emtype.name, emfield.name)
      
     ## @brief Generate a columns_fieldtype dict given a rel2type EmField
     # @todo do it
     @property
     def _relation_pk(self):
-        return ('id_relation', EditorialModel.fieldtypes.pk.EmFieldType())
+        return (MySQL.relation_table_pkname, EditorialModel.fieldtypes.pk.EmFieldType())
     
     ## @brief Returns a dict { colname:fieldtype } of relation table columns
     @property