cursor_bintype: only allow CSUD query in exec-params

According to bug #3002
only SELECT, UPDATE, INSERT and DELETE are safe to use with
PQExecParams() . So, disable any other SQL commands.

TODO: support EXECUTE queries as a special case.
cursor_bintype: fix error path for ExecParams calls

We had to set res = -1 , so that the Postgres error would propagate
into a pythonic exception.