Implemented trapped chests & others

+ Added trapped chests
* Fixed a bunch of bugs in the redstone simulator concerning wires and
repeaters
* Other potential bugfixes

I hereby present to xoft, ONE METRIC TON PRECISELY -----------------
-------------------------------  of code to review.

With thanks.
a_Chunk, the first parameter, is either the chunk where the block has changed (and so redstone is already marked dirty) or a neighbouring chunk, in which case it is marked dirty a few lines up.