(e.g. front of sofa faces you)

to use on_rightclick instead, for consistency with other parts of minetest,
minetest_game, etc.

requires unified dyes commit b0ccff16 or later

side effect:

I added a third shade of the formerly-white checker background
that alternates with the colored overlay.  The colored overlay
follows the standard full Unified Dyes palette.

* Don't trigger global variable warning.
* Change form name to avoid possible bugs in the future.
* Actually (opt-)depend on screwdriver mod.

as a side effect, this also fixes the bug where you couldn't
stack beds to form "bunk" beds.

Place a bed, right-click it with dye to color it.

Place two beds side by side and they'll form a king-size bed, which
you can right right-click with dye to color.

Place a regular bed, then right-click it while wielding another
regular bed (i.e. as if you were trying to place it) and, if there
is room above the first bed, the second will be placed on top and
the bedposts on the bottom one will extend to reach it.  Color
either of the two by right-clicking with dye.

Shift-right-click forces placement of a regular bed without trying
to stack it into bunks.

Right-click while NOT wielding a bed or dye will attempt to let you
sleep (via default beds code).

craft and place an oak shutter first, then right-click it with
dye to color it.  dig to get back the oak + dye.