[cairo] Tessellator performance patch

[Rafael Villar Burke]

> This could probably be clearer using
> #define not_top_precision(i)   ((i) < (INT32_MAX >> SUBPIXEL_PRECISION))
Oh, well, rather:
#define not_top_precision(i)   ((i) < (UINT32_MAX >> SUBPIXEL_PRECISION))

-- Rafael