[cairo] Disabling antialiased shape drawing

[Robert O'Callahan]

I'm glad to see this.

On Wed, 2005-08-03 at 23:57 -0500, Billy Biggs wrote:
>    2. The API can be safely ignored by backends that do not require this
>       setting, such as the PS or PDF outputs.

Making this API non-mandatory means that an application that wants to
use supersampling has to know, for each surface type it uses, whether or
not the surface type really supports this API. But such applications
already need to know which surface types need supersampling, so I guess
this is OK, as long as a surface type's support for this API is
considered part of the interface and isn't removed in the future.

Rob