Update to latest glext headers, add new extension strings, fix one order bug

git-svn-id: svn://svn.code.sf.net/p/irrlicht/code@4571 dfc29bdd-3216-0410-991c-e03cc46cb475
Add intersect method to create intersect box, provided by hendu

git-svn-id: svn://svn.code.sf.net/p/irrlicht/code@4572 dfc29bdd-3216-0410-991c-e03cc46cb475