deleting dependencies

Hi,

I've been looking at the dependency API and I notice that there is a
function to delete ALL dependencies on an object and a function to add a
dependency, but there doesn't seem to be any way of deleting a dependency
between two _particular_ objects.

Is there any other way of doing this other than manually deleting the row
from the pg_depend table?

I'm messing about with changing column type and I need to drop the
dependency on the old type and add the dependency on the new type....

Chris