Open doors when right-clicking a door with a door.

Open doors when right-clicking a door with a door.

And similarly, if we wield a door and right click any node
that has an on_rightclick() handler, call the handler
instead.

Just to be on the safe side, assure that none of this
code runs when right-clicking an entity or player, which
would likely crash the server.

Fold in PR #831 as well - prevent server crash on door
place on unknown blocks, by @tenplus1.