Fixes with respect to sector special touching and slopes

Some important stuff.

* SF_TRIGGERSPECIAL_TOUCH now actually works. Previously, it abandoned the loop early if ANY bounding sector didn't have that sector flag, which it likely didn't - only checking one extra sector's worth of FOFs. Also, the teleport handling there is more robust, and actually bails out if you teleport, instead of just awkwardly continuing through the loop.
* SF_TRIGGERSPECIAL_TOUCH now works for each time thinkers, too.
* Fixed a bug with being able to go under lava because P_CheckSolidLava doesn't take slopes into account.
* Also, P_CanRunOnWater supports slopes now too.
* Quicksand supports slopes and reverse gravity now.
* Space Countdown supports slopes now.

Also, an experiment behind a #define which currently isn't turned on:

* UNDER A #define, "SECTORSPECIALSAFTERTHINK", WHICH IS CURRENTLY TURNED OFF, BUT I WILL WANT TO TURN ON IN INTERNAL: Moved sector touch handling to P_PlayerAfterThinker (from P_PlayerThinker before movement). Allows for being able to trigger moving slope sectors that are going down, most specifically lava (didn't matter in RVZS in 2.1 because you could clip through the sides and go underneath the lava, causing damage - a sloped testwad version of that prevented going underneath.) Also fixes one-frame standing on deathpits before you die. Basically means sector triggers effectively happen one tic earlier, since it's after movement.

See merge request !131

Ping-related code fix

Somehow, the part of the netcode for calculating the players' pings in a netgame frequently gets the concepts of nodes and players mixed up, which is probably not a good thing. This branch of course fixes those slipups.

I originally based this branch on master to be merged to it (since it only fixed issues on the host's side), but after finding another issue with clients receiving PT_PING from the server, I decided to make this a merge to next instead.

See merge request !193

Ld414 invalid sound fix

This fixes Linedef type 414 crashing the game if an invalid sound number was supplied to it (this can happen if you, say, scrambled THZ2's textures *cough*), whether or not the "Repeat Midtexture" flag is checked.

See merge request !196

Fix for Lua's "PlayerSpawn" hook

This fixes how functions for the "PlayerSpawn" Lua hook aren't called when the player respawns at a starpost instead of at a map thing start.

(Note to Lua scripters who may want to adjust their scripts accordingly with this in future, checking if `player.starposttime` is non-zero is the best way to detect if you're spawning at a starpost or not.)

See merge request !198

Record Attack ghosts scale fix

This fixes how changes to the player's scale are recorded in Record Attack demos, so ghosts of your demos don't disappear when they attempt to change to scales >= FRACUNIT (if they didn't change scales at all they were unaffected).

Have some gifs for comparison:
* A demo recorded without the fix: https://dl.dropboxusercontent.com/s/tk9x8nptzhw7yb1/srb20106.gif
* A demo recorded with the fix: https://dl.dropboxusercontent.com/s/b4h4iuiwbh0voos/srb20107.gif

See merge request !197

This is probably a leftover from how scaling worked in v2.0 I take it

Had to make P_MobjReadyToTrigger non-inline for this fix though, because the compiler was being stupid

Fix for screenshots taken in OpenGL with resolution 1366x768

Fix for this bug: https://mb.srb2.org/showthread.php?t=39882 (also reported here: https://mb.srb2.org/showthread.php?p=793077#10)

This is basically porting GZDoom's own fix for the same issue (I stumbled on a Zandronum thread about the same issue from google images, and one user mentioned GZDoom had fixed it): https://github.com/doomtech/gzdoom/commit/d31a0b77fd19dae611166265acabe666c7ab1c59

See merge request !192

This is based on GZDoom's own fix for the same issue, had to add support for glPixelStorei first though

Hotfix: Lua thinkers.iterate

Update to v2.1.19

It should says what on the tin.

See merge request !190

Ignore askinfoviams

Turns out PT_ASKINFOVIAMS is an obsolete packet type anyway, the MS doesn't send it at all. So let's just ignore it in the netcode then. (the online page just acts like a client and sends PT_ASKINFO, and is not part of the MS itself)

See merge request !191

Disable gettext

Disable Gettext support for Mingw32 builds

See merge request !154

Netcode hotfix

Various netcode fixes are included in this branch. Most important of all of course is a fix for the Net_CloseConnection invalid node -32769 detected message thing, or rather what actually caused that to occur.

It's a merge to master since everything here should be compatible with 2.1.18: the only main changes are related to recieving packets (whether you're the host of a netgame or a client), which AFAIK shouldn't cause desyncs if you played with these fixes on a 2.1.18-hosted netgame (or hosted a netgame with the fixes and 2.1.18-using players join you).

See merge request !185

A bunch of bugfixes about too many wads in netgames

Fixes:
* Having bunch of music WADs added and then breaching the file limit(s) through joining a server with important files added. http://mb.srb2.org/showthread.php?t=42662
* Having a bunch of music WADs added, joining a server, and then breaching the file limit(s) when the server adds a file. https://mb.srb2.org/showthread.php?t=34664
* Informing the adminplayer whenever they try to send a request addfile net command but the file limit(s) are reached.

Done into next because I might as well be 100% safe, even though this could probably work on master as well.

See merge request !187

Missiles 'n slopes

Fixed that thing where missiles like sliding up slopes for some reason.

This isn't a 1:1 fix compared to non-slopes - missiles still like stepping up over the borders of sloped sectors and will continue going as long as they never touch that ground again, whereas they can never step up on flat ones - but this fixes the most egregrious issue.

See merge request !181

Cleanup part 2, make ye old 2.1.18 warning a debugfile only message, and make the node == -1 have its own debugfile only message too

Also get rid of a stray newline

textcmd[0] for PT_NODETIMEOUT can't hold anything < 0 anyway, and you'd probably have to really try to get >= MAXNETNODES

Display node's IP when printing the "sending file to node n" message, if noticedownload is turned on