Changed where we get block IDs from for GatewayBlockFilter. DDProperties
always has correct block IDs. It's only item IDs that are modified by
Forge so that DDProperties is wrong.
Fixed a bug I introduced during my previous commit that caused solo
rifts to spread and rifts with neighbors not to spread. Also cleaned up
the code a bit to cut back on the number of mysterious random rolls we
were using and commented the code.