Allows the placement of stone path and concrete on landfill. Also allows the mining of the stone-path and concrete and restores the underlining landfill.

Known Issues (probably won't fix)

When placing stone path on top of landfill, the landfill will be subtracted from the inventory. The rising inventory text doesn't reflect this.
If the inventory is full, the landfill will be dropped and becomes free landfill.

When mining a larger area with stone path on top of landfill, the restored underlying landfill will be mined before the next stone path.