Put HTTP downloading on a background thread

See merge request !2322

Fix segfault due to leftover ztargetfocus when switching maps

Closes #1333

See merge request !2573

Fix plane offsets overflow in the software renderer

Closes #1322 and #1227

See merge request !2575

Correctly force Sonic in the tutorial (resolves #1331)

Closes #1331

See merge request !2571

Fix segfault when switching perfstats screen before sampling is done

See merge request !2576

Fix io.open() crashing the client sometimes

See merge request !2578

Fix some components of ticcmd being blocked in IntermissionThinker

Closes #1330

See merge request !2572

Increase ps_samplesize default value to 175

See merge request STJr/SRB2!2562

Remove MAXRADIUS adjustment from bounding box calculations

See merge request STJr/SRB2!2566

Fix blocknode iterating and simplify P_BlockThingsIterator

Closes #1323

See merge request !2565

Merge branch '1324-next-post-pre3-mobjremoved-hook-is-broken-always-immediately-errors-into-please-check-valid' into 'next'

Fix #1324

Closes #1324

See merge request !2564

Revive Haiku build

See merge request !2537

This was added by the Doom developers to work around the issue where
objects were not linked into all blockmap cells they were touching, and
instead just the one at the object's center. Since this is no longer
the case after commit 41613d89,
this adjustment is no longer necessary.

There was no reason to do what I did, since the loop only needs to hold
a reference to the next block. This reverts the function to how it was
before 7469a627, but holds the
reference properly.

Fix performance regressions in addon loading

See merge request !2560

Fix segfault when accessing skin from lua on a delayed removal

See merge request !2558

Fix HWR_ClearLightTables being called too late

See merge request !2557

extracolormaps own the OpenGL-specific light table data, so that has to be freed earlier.

Fix crash when spawning a BOT_2PAI on a 2D map

See merge request !2552

Fix sector portal heights

Closes #1309

See merge request STJr/SRB2!2545