Broken by 6bc4cad0, e.g.
  minetest --worldname world
would be parsed as
  minetest --worldname --worldname

Broken by 6bc4cad0 because database-redis.h
depended on settings.h to include filesys.h.

Caused by a020d1b6.

This also cleans up settings a bit

Also check for (this == &other) before locking mutexes.

Also removed 2 unused functions.

Also clean up some related things.

Protocol version bump.

Catch some error situations when mod used without thinking about it

See: https://github.com/minetest/minetest/issues/1525

Background
Wuzzy2: If you attempt to spawn a L-system tree with minetest.spawn_tree, you can make Minetest crash if it is attempted to pop an empty stack.

ShadowNinja: This shouldn't cause a segmentation fault, but it should throw a Lua error

Commit Description
This commit throws a Lua error instead of causing a segmentation fault. The server will still "crash" but will include a Lua backtrace.

L-Systems fix randomness
Unless a random seed is provided (via Lua treedef) seed the PRNG with a different seed for each tree
Resolves: https://github.com/minetest/minetest/issues/1469

Fix l-system crash when treedef random_level not set by Lua

10 seconds in PvP is very long and annoying.