In the calculation of y_start,
when 'column height max' was large it caused
nmin.Y + max_height > nmax.Y - max_height
Now, in this situation y_start is set to the
midpoint between nmin.Y and nmax.Y

Limit y0 and y1 to between nmin.Y and nmax.Y,
otherwise index calculation, which has no checks for limits,
places them at unwanted locations in the voxelmanip

Android had a linker error since commit:

31e0667a "Add Lua interface to HTTPFetchRequest"

Fixes #3766. Thanks to @MoNTE48 for reporting the bug.

As stated in this forum thread [1], I noticed that there is a
2 second interval in which inventory changes are shown on the
client. @yyt16384 found the source of these 2 seconds:
m_nothing_to_send_pause_timer is set to 2.0 every time there
are no changes to make, but this timer is not reset when
SetBlockNotSent or setBlocksNotSent are invoked. So in worst
case, the changed block will be sent over 2 seconds too late.

With this change, changed inventories are updated almost
immediately, but it causes additional connection load.

Newest leveldb commit breaks build.
With no fix in sight, there is no other way
than to fall back to the last working leveldb
revision, and hardcode it.

Workaround for upstream bug

https://github.com/google/leveldb/issues/340

Fixes #3719
Closes #3753

This allows mods to perform both asynchronous and synchronous HTTP
requests. Mods are only granted access to HTTP APIs if either mod
security is disabled or if they are whitelisted in any of the
the secure.http_mods and secure.trusted_mods settings.

Adds httpfetch_caller_alloc_secure to generate random, non-predictable
caller IDs so that lua mods cannot spy on each others HTTP queries.

Instead, perform a POST request with post_data.

Closes #3748

Fixes #3378
Closes #3751

Also, downgrade the error to a warning.

Previously you could steal a secure environment from a trusted mod by wrapping
request_insecure_environment with some code like this:

local rie_cp = minetest.request_insecure_environment
local stolen_ie
function minetest.request_insecure_environment()
	local ie = rie_cp()
	stolen_ie = stolen_ie or ie
	return ie
end

'cam_pos_nodes -/+ box_nodes_d' can exceed the range of v3s16
when a player is near the world edge using a large view range
This previously caused world to disappear
Create new function getBlocksInViewRange() called from
updateDrawList() and renderMap()
Correct code style throughout updateDrawList() and renderMap()

Commit

6a1670db "Migrate to STL containers/algorithms."

has replaced core::map<T, bool> with std::set<T>, but didn't update
the accompanying comment saying "value is dummy". This happened at
two places.

Fixes #3701.

Thanks @ExcaliburZero for noticing. Fixes #3698.

* Sky: rename Box => m_box and inline getBoundingBox
* Uniformize aabbox3d<f32> to aabb3f

This makes the functions a bit faster since they don't
have to recreate the tables every invocation, and makes
the code more readable.

Also, document `wallmounted_to_dir`.

The function was implemented but not documented in `lua_api.txt`.