Fix placement issues with red sandstone stairs / slabs

For some reason mojang decided to use new item IDs for these - they just needed to be added to ItemTable, and include them in a few conditions in BlockSlab.

To test:

* Stairs: just place them in any direction or inverted. Old behavior sticks them with a single orientation.
* Slabs: place two red sandstone slabs on top of each other, they should stack into a double slab. Old behavior leaves two single slabs, the second one floating above with a space in the middle.