Prevent building of any kind with non-buildable materials.

Horribly end portal glitches! :(
Fix bridge spell.
Try to copy entities along with replicated and cloned blocks.

Wheeeeeeee!
Superconvert now only replaces the target block's material.
Implement a separate restricted materials list.

Also put a check in to make sure we don't try and build with items,
ever.
Fix a glitch involving dropping spells out of wands.
TODO Update