The test now explicitly reads back from the framebuffer to sanity check that
texturing is happening as expected, and it now uses a fixed 2x2 texture instead
of redhand.png since redhand.png doesn't have a power of two size which can
cause the vertex buffer code to complain on hardware not supporting npot
textures.
Fixes some blending issues when using color arrays since we were
conflicting with the cogl_enable state + fixes a texture layer
validation bug.
Adds a basic textured triangle to test-vertex-buffer-contiguous.
This better reflects the fact that the api manages sets of vertex attributes,
and the attributes really have no implied form. It is only when you use the
attributes to draw that they become mesh like; when you specify how they should
be interpreted, e.g. as triangle lists or fans etc. This rename frees up the
term "mesh", which can later be applied to a concept slightly more fitting.
E.g. at some point it would be nice to have a higher level abstraction that
sits on top of cogl vertex buffers that adds the concept of faces. (Somthing
like Blender's mesh objects.) There have also been some discussions over
particle engines, and these can be defined in terms of emitter faces; so some
other kind of mesh abstraction might be usefull here.
