(may need to add support for directx8 and software?)

-made terrainNode use DynamicMeshBuffer, so it can use 32bit buffers. (no more size limits now on terrains!!! )
if the terrainNode loads an image over 256x256, it is set to 32bit, smaller sizes will use 16bit for better speed.

git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@1515 dfc29bdd-3216-0410-991c-e03cc46cb475