[cairo] Quartz backend fix

[Chris Wilson]

On Sun, 2009-08-09 at 22:40 +0200, Andrea Canciani wrote:
> Today I tried compiling cairo from git on my iBook and found out that
> the quartz backend was broken.
> Chris already fixed most compilation errors, here is the fix for the last one.

Many thanks, Andrea, pushed to master. Please let us know how the quartz
backend is currently faring on the test suite.
-ickle