Improve (re)spawn, add cache_block_before_spawn and max_spawn_height settings
Fix win32 jthread implementation
Fix small mistake in Lua API docs
Fix paralax occlusion setting
Move script_run_callbacks to Lua
Dungeongen: Create dungeon gen tuneables; add desert temples for Mapgen V6
EmergeManager: Fix Lua mapgen override param handling
Fix leak and possible segfault in minetest.set_mapgen_params
Fix shaders on some GPUs
Mapgen Indev: Fix segfault in cave generation due to uninitialized variable
Optimize shaders code. Add settings at compile time.
Check if width, height or start index of a list[] is negative
Add Lithuanian translation.
Implement search tab and version picker
Add configurable font shadow.
Add 'on_prejoinplayer' callback
Make line_of_sight return blocking node position
Fix a bug in GenericCAO GENERIC_CMD_UPDATE_POSITION parsing.
Implement httpfetch module and initialize it from main()

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.)
Rewrite client media download and support hash-based remote download

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.