Improve message about drill control

The message to "hold shift" makes an unwarranted assumption about the
user's keybindings.  Messages from the server should refer to a key's
game function, rather than its extragame identity.
Fix drill charge usage

The drills weren't taking the variable usage cost into account (either
the per-type base cost or the per-mode multiplier) when deciding whether
they have sufficient charge to use.  This could cause them to overshoot in
charge usage, although they would then clamp to zero rather than record
negative charge.  Also, for the Mk1 drill where the cost was assessed
correctly, the drill would refuse to discharge to exactly zero charge.
Fix drops for active machines

Active machine nodes need to drop their inactive counterpart.  Some were
missing that declaration.
Fix chest log messages

All log messages about moving stuff in/into/from chests described them
as "locked", whether the chests are locked or not.  Remove that word,
so the messages make no claim about lockedness.
Fix flashlight light node declarations

The light and light_off node types should be not_in_creative_inventory,
and should drop nothing.
Fix flashlight's light generation

The flashlight was lighting the wrong node, 1 m east of the player's lower
half, thus getting no light if the player is adjacent to an eastern wall.
Restore the old 1 m above, that coincides with the player's hands.

There was a problem with light from the flashlight getting stuck in
the map.  This arises because the flashlight's light value was 15, the
reserved value that the engine uses for sunlight.  Moving the flashlight
upwards, by jumping while it is equipped, would cause the node below it to
acquire a bogus sunlit state.  Fix this by reducing the flashlight's light
value to 14 (LIGHT_MAX), which is the maximum permitted for non-sunlight.

The light_off node type is not required.  With the light value limited
to 14, mere removal of the light node suffices to correctly recalculate
lighting.
Fix discharge of flashlight and sonic screwdriver

These two tools wouldn't discharge all the way to zero through use,
unlike most chargeable items.

Incidentally remove a duplicate of the check_for_flashlight() function.
Fix search for operating flashlight

Having a never-charged flashlight in the hotbar earlier than a charged
flashlight prevented the charged flashlight being found.