use string parsing to determine stairs

Unfortunately stair/slab groups are pretty inconsistent so using the
name (ID) of them works best. Raw string parsing is bad but it is
actually more reliable then using the group.

redefinitions/moreblocks_rotation.lua

@@ -104,7 +104,7 @@ end
 -- Determine all stairs and slabs and put them into the respective tables.
 for name,definition in pairs(minetest.registered_nodes) do
     local from_moreblocks = definition.mod_origin == 'moreblocks'
-    local stair = definition.groups.stair
+    local stair = string.match(name, ':stair_') ~= nil
     local slab = string.match(name, ':slab_') ~= nil
 
     if stair and from_moreblocks then table.insert(stairs, name) end
@@ -114,6 +114,7 @@ end
 
 -- Iterate over all stairs and override the broken on_place function.
 for _,name in pairs(stairs) do
+    print(dump(name))
     override_item(name, {
         on_place = function (itemstack, placer, pointed_thing)
             if pointed_thing.type ~= "node" then return itemstack end