Initialize all memories to 0
Put the chisel temps at the top level

This makes it easier to match what I'm in the process of modifying
Chisel to output.
Put the Chisel temps in _chisel_temp_

The old name was _llvmflo_..., which is not really sane seeing as how
we're going to be modifying Chisel in order to output temporaries to
the VCD file.
Don't try to write back INIT nodes

This doesn't make any sense at all, as there's no value associated
with them.
Handle write-enable in WR nodes

I guess I forgot to handle write enable, which is now handled by a
read-modify-write cycle.  There isn't a test for this now, but
chisel_mem.bash fails if we diff against temp nodes, which will be
coming in a future Chisel release (that's how I found the bug, but my
current implementation is pretty hacky).