Add driver attribute element for AntiAliasing level. This allows to check whether the driver has AA enabled, and which level.
Fix AA setup for OpenGL under windows, where the extension was missing and no error came up due to unsupported feature request. Now, the driver recognizes the missing support and properly sets AA to 0.

git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@3491 dfc29bdd-3216-0410-991c-e03cc46cb475