Fixed third-person camera movement bug in the viewer.

Fixed third-person camera movement bug in the viewer.
Fixed a bug that caused the viewer to render "random" polygons in some special cases.
ASE: Added parsing support for *GROUP nodes. Improved light & camera handling (still WIP). Fixed a bug that was caused by a recent change. Improved logging.
Updated PretransformVertices. The step works now (and supports line and point meshes). Important: The position of the step in the pipeline has changed. No unit test yet.
Minor fixes to SortByPType. Added a config option that allows users to specify which primitive types they don't need.
Added WIP version of an Irrlicht Scene Loader (.irr).
Added a small helper class ("BatchLoader") to make it easy for loaders to load subsequent meshes from external files (needed for irr and lws).
Added test models for IRR. Added dwarf.x from the Irrlicht repository (readme included) to the test X files.
[Current TODO: Fix bugs in: AC, 3DS, LWO. Finish MDR and OG. Implement: IRR, LWS. Write some more ut's ... ]

git-svn-id: https://assimp.svn.sourceforge.net/svnroot/assimp/trunk@197 67173fc5-114c-0410-ac8e-9d2fd5bffc1f