Glass and non-Glass slabs can't be stacked together

[sirrobzeroone]

Its not possible inside the minetest engine to have a node which has half the properties of "normal" and half the properties of "glasslike". Unfortunately this means if I include code to allow the stacking of glass and non-glass slabs you get some interesting visual effects in game.

Summary:

• Normal slab on glass slab - slab appears as top normal slab with some strange graphic overlay.
• Glass slab on normal slab - slab appears as top glass slab ie full glass block.
• For example of above place "glass" slab on "obsidian glass" slab and vice versa the node will take on the look of the top most slab, this seemed minimal issue so left this combo okay