Don't move the mouse anymore when the mouse hasn't moved.
This was sometimes confusing because events are only caught inside the window (at least on Windows),
which lead to the node moving seemingly randomly when the mouse was outside.
Also added a few more comments to mention CursorControl as an alternative.
git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@6308 dfc29bdd-3216-0410-991c-e03cc46cb475