cairo: update git to 1.3.9

cairo: update git to 1.3.9
update snapshot to 1.3.8, from its news file:
After the bug fixes in 1.3.6, we're back to our original program of
weekly snapshots, each one faster than the one from the week
before. Cairo 1.3.8 brings a 2x improvement in the speed of rendering
linear gradients (thanks to David Turner), and a significant reduction
in X traffic when rendering text (thanks to Xan Lopez and Behdad
Esfahbod), making cairo behave very much like Xft does.
A few other things in the 1.3.8 snapshot worth noting include a more
forgiving image comparator in the test suite, (using the "perceptual
diff" metric and GPL implementation by Hector Yee[*]), a bug fix for
broken linking on x86_64 (thanks to M Joonas Pihlaja) and an even
better implementation of _cairo_lround, (not faster, but supporting a
more complete input range), from Daniel Amelang.