Update to Blender 2.71

2.71 upgrades to MSVC++2013, so we can use the newfangled log2. This fixes
a rounding bug as well :)
More log tweaking...
Basic collision modifier

This basic collision modifier supports sphere bounds and triangle mesh
bounds. We still need to decide if things like calcSphereBounds belong in
libHSPlasma or if they should live in korlib.