django 1.6, add unique_together constraint name.

creation.py

class CustomDatabaseCreation(BaseDatabaseCreation):
    def sql_create_model(self, model, style, known_models=set()):
        final_output, pending_references = super(CustomDatabaseCreation, self).sql_create_model(model, style, known_models)
        
        # get output generated by parent class for unique_together.
        for field_constraints in opts.unique_together:
            line = ('    ' + style.SQL_KEYWORD('UNIQUE') + ' (%s)' %
                ", ".join(
                    [style.SQL_FIELD(qn(opts.get_field(f).column))
                     for f in field_constraints]))
            try:
                constraint_name = model._meta._index_names[field_constraints]
                replacement_line = ('    CONSTRAINT %s ' % constraint_name 
                    + style.SQL_KEYWORD('UNIQUE') + ' (%s)' %
                    ", ".join(
                        [style.SQL_FIELD(qn(opts.get_field(f).column))
                         for f in field_constraints]))
                # add the name in...
                final_output = final_output.replace(line, replacement_line)
            except (KeyError, AttributeError, TypeError):
                # KeyError - index name not defined for tuple
                # AttributeError - _index_names not defined on model._meta
                # TypeError - not using hashable key (e.g. list instead of tuple)
                continue

        return final_output, pending_references