test-cogl-materials: Add a test using the maximum number of layers

test-cogl-materials: Add a test using the maximum number of layers

This adds a test which creates a material using the maximum number of
layers. All of the layers are assigned a white texture except the last
which is set to red. The default combine mode is used for all of the
layers so the final fragment should end up red.

Currently Cogl doesn't provide a way to query the maximum number of
layers so it just uses glGetIntegerv instead. This might cause
problems on GLES 2 because that adds additional restrictions on the
number of layers.

http://bugzilla.openedhand.com/show_bug.cgi?id=2064