-add client states to avoid server sending data to uninitialized clients
  -don't show uninitialized clients to other players
  -propper client disconnect handling
Minor comment fixes in server
Minor bugfixes in connection
  -improved peer id calculation
  -honor NDEBUG flag
  -improved disconnect handling
  -increased initial send window
Remove some dead code

because cmake is unable to parse it's own lists properly

This can solve numerous problems such as:
http://www.cmake.org/Bug/view.php?id=13959
http://www.cmake.org/Bug/view.php?id=14601

If pkg-config or freetype2.pc is not found, then fall back to the
FindFreetype.cmake module logic.

Restrict to UNIX since I only tested it here.

Move most of the media-related code in client.cpp into a new class
ClientMediaDownloader (clientmedia.cpp, clientmedia.h). Among other
things, this class does the following things:

- Download [remote_server][sha1] instead of [remote_server][name]. This
is to support servers that provide the same file name with different
contents.
- Initially fetch [remote_server]index.mth. This file should follow the
Minetest Hashset format (currently version 1) and contain a list of SHA1
hashes that exist on the server.
- The list of needed SHA1s is uploaded (via HTTP POST) when index.mth is
requested, so servers can optionally narrow down the list to the needs
of the client.
- If index.mth is missing (HTTP response code 404), we enter compat mode,
fetching [remote_server][name] as before this commit.
- remote_server can now contain multiple servers, separated by commas.
The downloader code attempts to split requests between the different
servers, as permitted by each server's index.mth. If one server claims
to have a file but actually doesn't (or something fails), we ask a
different server that also claims to have it.
- As before, when none of the remote servers provide a particular
file, we download it via the conventional method, i.e. using
the minetest protocol: TOSERVER_REQUEST_MEDIA / TOCLIENT_MEDIA.
- Bugfix: Every downloaded file's SHA1 is now verified against the SHA1
announced by the minetest server (before loading it and inserting it
into the file cache).
- Bugfix: Only send TOSERVER_RECEIVED_MEDIA when we actually have all
media. This should fix #863.

Add curl_parallel_limit setting that will replace media_fetch_threads in
a later commit.

Fix a typo in MutexedQueue::pop_back() that made it impossible to compile
code that used this function. (Noticed this while implementing httpfetch.)

On the lua side, notably minetest.env:<function>(<args>) should now
be replaced by minetest.<function>(<args>).
The old way is and will stay supported for a long time.

Also:
Update and clean up lua_api.txt (by celeron55)
Move EnvRef to lua and remove add_rat and add_firefly (by kahrl)
Add separate src/util/CMakeLists.txt, other minor fixes (by kahrl)

This commit broke RUN_IN_PLACE

Spawn single particles or make use of ParticleSpawner for many randomly spawned particles.
Accessible in Lua using minetest.spawn_particle and minetest.add_particlespawner.
Increase Protocol Version to 17.

Conflicts:
	src/clientserver.h