When a trapdoor is mounted upside down, to make its top surface flush
with the floor above when closed, it is necessary to have some way to
climb through the trapdoor node when it's open.  Making it climbable
like a ladder satisfies this need.  It is somewhat realistic, as a real
trapdoor can have a ladder segment mounted on one face.  When the trapdoor
is mounted in its default orientation, making the bottom surface flush
with the ceiling below when closed, the climbability when open is not
strictly necessary, but is still a convenience.

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.

The left-handed recipes for axes were using default:stick instead of
the group:stick used by all other tool recipes.

Cotton plants used to drop strings, now they drop farming:cotton. Some mods (namely, throwing) still use farming:string, therefore we need farming:string to be equal farming:cotton.

Add spaces around operators in boat mod code, fix a problem with boat staticdata, fix a crash that can occur with boat going over unknown nodes.

- API {farming.register_hoe(), farming.register_plant()}
- Fertilities -> Plant only grow on soil with a fitting fertility, e.g. Wheat only grows on grassland, while cotton grows in deserts and grassland)
- New soil: Desert Sand
- Place seeds instead of plants

This adds protection for furnaces (when the area is protected, so it the
furnace).
Also made the codes a bit shorter..

These changes allow players to punch up old bones or their own.
If there is no area for bones, drop the items instead of delete.
Notify the player where he died, so he can find them again.