Fix crash when placing log pile in pit kiln.

ItemLogs was casting the TileEntity to TileEntityLogPile without first
checking to make sure that it was one.
Crashfix for leatherworking with the crafting grid.

This is a workaround for a Forge bug that will be hopefully resolved soon (the issue on their github is 732).
Merge pull request #233 from mayaknife/kilnLogpileCrash

Fix crash when placing log pile in pit kiln.