Fix naming scheme for occlusion queries. Since those are not to drop, but are stored in the driver and can be removed by the according removeOcclusionQuery call, the name should be addOcclusionQuery instead of createOcclusionQuery.
Added an example showing a very simple occlusion query setup.

git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@3628 dfc29bdd-3216-0410-991c-e03cc46cb475