somehow, now we are just bypassing Ogre::Terrain for the colour map and
passing it directly to the material, which makes more sense
performance-wise anyway
be almost impossible to make a derived class of TerrainMaterialGeneratorA
because of the many classes it contains and the inter-relationships
between them; just adding the whole source makes it a lot easier to modify
if we decide to update this source from OGRE upstream at any point
(which seems unlikely), we can take the diff from this commit on
to see the changes we did to the material generator