Fix potential crash by floating point error

Normalizing a null quaternion is a bad idea, and setOrientation()
happens to normalize its argument internally. Thanks for not documenting
this, Ogre.
Enable simpler camera tracking again

If there's a lot of lag (e.g. running a debug build, or on a slow
computer, ...) the smooth camera can and will jump at random until it
gets stuck looking at the sky while twitching madly.
And it causes noticable jitter even with small framerate drops.
Enable on-the-fly .bullet generation for Meshes