Avoid some broken calculations for IBoneSceneNode positions.

Avoid some broken calculations for IBoneSceneNode positions.

This is based on bugreport #458 reported by viwrap who also made a nice test-case model.
Note: While solution seems to work and would even be faster, I'm not 100% sure yet if there are no downsides.
The other solution seems to regard last column in matrices - thought I don't think we ever set or use that.
And I also haven't found out yet _why_ the original solution goes wrong.
But animation system uses right-hand quaternions unlike rest of Irrlicht which is obviously a bit dangerous, will have to check the conversions some day.

git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@6438 dfc29bdd-3216-0410-991c-e03cc46cb475