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

Removed unused camera_position and camera_direction fields from Client. Moved ClientEnvironment::drawPostFx to ClientMap::renderPostFx -- this will make the camera management classes easier to write, as ClientMap already knows the camera position but ClientEnvironment doesn't and has to be told about it. This also eliminates the need for Client::getEnv(). Made the post effect color a content feature defined in content_mapnode.h.

New map generator added (and SQLite, messed up the commits at that time...) (import from temporary git repo)

Reduced server CPU usage on NodeMetadata step()s. Also furnace now cooks while no players are near it.

--HG--
extra : rebase_source : 7260636295d9068fbeeddf4143c89f2b8a91446c

a work-in-progress map modified callback interface (committing because i want to merge the fence stuff)