1) The active camera.
2) Receiving input.

This allows example 09.Meshviewer (with two cameras) to work as expected.  Replace the magic numbers in that example with enumerated values.

This patch also exposes ISceneNode::SceneManager through a public getSceneManager() API.

git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@1974 dfc29bdd-3216-0410-991c-e03cc46cb475