fix broken screwdriver mode2

Screwdriver Mode 2 was somewhat broken: Rotation around a side axis was mostly unpredictable, often coming up with a completely different face in front (try rotating stairs around a horizontal axis: it's more like a slot machine, you never know which side will come up and how it's rotated).

I've rewritten the mode2-handling and removed some clutter, it now works like expected: Nodes are rotated consistently clockwise in 90 degree steps for all sides and around any axis.
Comments are added so you may get an idea what's going on.

Oh - and I've added a check so that item_wear is disabled in creative mode - if that's something to be decided separately, I'll put it in a separate pullreq...