Screwdriver: disallow rotation with on_rotate = false

Other screwdriver mods, or mods that cause rotation, might operate without the screwdriver mod loaded and have `screwdriver.disallow` unavailable.
This allows nodes to default to full-disallow rather than full-rotation in such a situation.

game_api.txt

@@ -348,7 +348,7 @@ To use it, add the `on_screwdriver` function to the node definition.
  * `new_param2` the new value of param2 that would have been set if on_rotate wasn't there
  * return value: false to disallow rotation, nil to keep default behaviour, true to allow
  	it but to indicate that changed have already been made (so the screwdriver will wear out)
- * use `on_rotate = screwdriver.disallow` to always disallow rotation
+ * use `on_rotate = false` to always disallow rotation
  * use `on_rotate = screwdriver.rotate_simple` to allow only face rotation
 
 

mods/screwdriver/init.lua

@@ -64,6 +64,7 @@ screwdriver.handler = function(itemstack, user, pointed_thing, mode, uses)
 		end
 	else
 		if not ndef or not ndef.paramtype2 == "facedir" or
+				ndef.on_rotate == false or
 				(ndef.drawtype == "nodebox" and
 				not ndef.node_box.type == "fixed") or
 				node.param2 == nil then