image: Implement high level interface.

Write a dedicated compositor for pixman so that we avoid the
middle-layer syndrome of surface-fallback. The major upshot of this
rewrite is that the image surface is now several times quicker for glyph
compositing, which dramatically improves performance for text rendering
by firefox and friends. It also uses a couple of the new scan
convertors, such as the rectangular scan converter for rectilinear
paths.

Speedups
========
image-rgba          firefox-talos-gfx-0    342050.17 (342155.88 0.02%) -> 69412.44 (69702.90 0.21%):  4.93x speedup
███▉
image-rgba                        vim-0    97518.13 (97696.23 1.21%) -> 30712.63 (31238.65 0.85%):  3.18x speedup
██▏
image-rgba                  evolution-0    69927.77 (110261.08 19.84%) -> 24430.05 (25368.85 1.89%):  2.86x speedup
█▉
image-rgba                    poppler-0    41452.61 (41547.03 2.51%) -> 21195.52 (21656.85 1.08%):  1.96x speedup
█
image-rgba       firefox-planet-gnome-0    217512.61 (217636.80 0.06%) -> 123341.02 (123641.94 0.12%):  1.76x speedup
▊
image-rgba             swfdec-youtube-0    41302.71 (41373.60 0.11%) -> 31343.93 (31488.87 0.23%):  1.32x speedup
▍
image-rgba         swfdec-giant-steps-0    20699.54 (20739.52 0.10%) -> 17360.19 (17375.51 0.04%):  1.19x speedup
▎
image-rgba                       gvim-0    167837.47 (168027.68 0.51%) -> 151105.94 (151635.85 0.18%):  1.11x speedup
▏
image-rgba          firefox-talos-svg-0    375273.43 (388250.94 1.60%) -> 356846.09 (370370.08 1.86%):  1.05x speedup

1 files changed, 0 insertions, 0 deletions

diff --git a/test/leaky-dashed-rectangle.ref.png b/test/leaky-dashed-rectangle.ref.png
index c0ba7b2c0..05f45846a 100644
--- a/test/leaky-dashed-rectangle.ref.png
+++ b/test/leaky-dashed-rectangle.ref.png