Added feature (heatblades are fire source when turned on)

Finally got around to fixing a lingering bug.  When switched on,
heatblades can be used for any task that requires a source of flame
(lighting a cigar, pipebomb fuse, etc.), and consumes no additional fuel
in doing so (the thing is already glowing hot, and using fuel
constantly).
Add heatblade menu to lit torch (fixes #2857)

I know the torch isn't a heatblade, but the menu is the same and it's a
tiny fix anyway so I thought I'd stick it here.  Also set charges per
use on torch to 0 so it didn't screw up the iuse menu, the torch losing
a charge from being extinguished was already covered in the iuse entry
and was essentially double-billing people.