[cairo] PATCH: Use floats instead of doubles in some spline calculations for improved performance

[Marko.Kuukkanen at tieto.com]

>Could you provide some error analysis to show when your patch is applicable and
>the accuracy sufficient?

No formal analysis has been made, but I ran canvas performance test
(http://dl.dropbox.com/u/1865210/mindcat/canvas_perf.html - on ARM and
rendered using Cairo) 15 times. During those tests _cairo_spline_error_squared
was called about 100 million times with randomized data and just once
there was one pixel difference between double and float versions.

Unfortunately I didn't record the used spline in that case and haven't been
able to reproduce that since.

--MarkoK--