[cairo] Cairo version now at 1.5.1

[Adrian Johnson]

Carl Worth wrote:
> But I also think I was unfair to call Vlad's work "24.8 work". I
> believe his code is just a #define away from supporting any of the
> options you propose above. So we can definitely explore things easily
> here.
> 
> That said, anybody have any interesting opinions in that discussion?

In the PS/PDF backends where 1 device unit is 1/72 inch there needs to
be enough precision to position objects to the accuracy of the printer
resolution.