Cannot create a datestamp field under postgres

The datestamp field is defined as type=int, length=11. When a datestamp field is added, this spec gets translated by db_add_field into the following query

ALTER TABLE {content_type_foo} ADD COLUMN field_bar_value int(11)

This query fails with a syntax error on postgres, because you cannot specify the numeric length for int fields in Postgres. It seems likely that the size parameter is unnecessary, since in MySQL it is only used for display padding and string compares.

Patch attached.