Fix bug #1856152, scaled oct tree nodes being incorrectly frustum culled.  Changed matrix4::transformPlane(), and removed transformPlane_new().  Tested following the procedure in the bug report, plus ran the other examples, and a small unit test.  However, my confidence isn't 100%, and it could be optimised, so more eyes would be welcome.

git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@1723 dfc29bdd-3216-0410-991c-e03cc46cb475