ERROR: cannot alter type of a column used by a view or rule

Hi,

I create this table:
create table teste (campo1 varchar(20));

And this view:
create view vteste as select * from teste;

When I try change the type of the column raise thir error:
db=# alter table teste alter column campo1 type varchar(30);
ERROR: cannot alter type of a column used by a view or rule
DETAIL: rule _RETURN on view vteste depends on column "campo1"

My question is: Who I can create a "select" no system catalog to return views with this column befor raise error?

Thanks,