Use numbers instead of iterators to traverse various vectors.

It isn't needed anymore, sending ICraftDefManager over the network has been obsoleted
by protocol version 7.

Fix style, refactor assert, use '"' instead of "\"",
replace code duplicating craftGetItemName, rename iterators.

This greatly increases crafting performance, especially in worlds with many mods.

Approved by @kwolekr.

Introduces a hash-type-layered fall-through mechanism, where every layer specifies one hash algorithm,
and the "deeper the fall", the more collisions to expect for the algorithm. One Craft definition
only resides at one layer, which improves speed for lower layers (and a complete fail), due to most
craft definitions residing at high layers.

Due to the fall-through design, the undocumented behaviour that later craft recipes
override older ones had to be weaked up a bit, but craft recipes with the same hash and layer
will still override.

Signed off by: ShadowNinja, kwolekr

Switch the license to be LGPLv2/later, with small parts still remaining as GPLv2/later, by agreement of major contributors

The huge item definition and item namespace unification patch (itemdef), see http://c55.me/minetest/wiki/doku.php?id=changes:itemdef