Fix Meshbuffer interface of md3 files. At least for some situations these should return the proper buffers now, and hence allow for stencil shadows and other things. We might need an animation update check, though, to handle multiple meshes.

git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@3968 dfc29bdd-3216-0410-991c-e03cc46cb475