Thanks, this clarifies things for me.
There's DROP ROLE IF EXISTS, which I'm using.
2012/6/22 Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
>
> Roles are not considered to be part of an extension: they really can't
> be, since an extension is local to a database while a role is global to
> the whole installation. As per the documentation, you're allowed to do
> CREATE ROLE in an extension script but it won't be managed by the
> extension mechanism.
>
> Not sure about a better solution to your problem offhand. It might be
> sane for the script to do CREATE ROLE IF NOT EXISTS, if we had that,
> which we do not :-(
>
--
Victor Y. Yegorov