Fix Bug 765: Add glMultiDrawElementsBaseVertex ; Restrict PointerBuffer usage to NIO only.

Code snippet for PointerBuffer usage:

Code snippet .. how to use PointerBuffer in this case:

IntBuffer indices = Buffers.newDirectIntBuffer(count);
indices.put(...); ...
indices.rewind();

final PointerBuffer indicesP = PointerBuffer.allocateDirect(1);
indicesP.referenceBuffer(indices);

-> glMultiDrawElementsBaseVertex(int mode, IntBuffer count, int type, PointerBuffer indices, int primcount, IntBuffer basevertex)