The material cache will now only set the special combine mode if the
texture only has an alpha component. The atlased textures will have
all four components so it will leave the combine functions at the
default. This increases the chances of batching between glyphs and
images.
When using the global atlas, the glyph from cairo is now rendered into
an ARGB surface rather than an alpha-only surface.
Instead of creating just two materials (one for texturing and one for
solid primitives) the pango renderer now maintains a cache of
pipelines. The display list can request a pipeline for a texture from
the cache. The same pipeline cache is used by all display lists so
that the pipelines can be shared. This avoids changing the texture on
the material during a paint run.
