Fix SWIG bindings

The bindings now compile and in Python a mesh can be extracted from a volume.
The only extractor currently bound is SurfaceExtractor<SimpleVolume, Material8>.

The bindings are still commented out in library/CMakeLists.txt by default.

library/PolyVoxCore/include/PolyVoxCore/SimpleVolume.h

@@ -36,6 +36,7 @@ namespace PolyVox
 	class SimpleVolume
 	{
 	public:
+		#ifndef SWIG
 		class Block
 		{
 			//Make Sampler a friend
@@ -129,6 +130,7 @@ namespace PolyVox
 			//Other current position information
 			VoxelType* mCurrentVoxel;
 		};
+		#endif
 
 	public:
 		/// Constructor for creating a fixed size volume.