gcc7 compile fixes (Fall through; spr2 var comparison)

See merge request STJr/SRB2Internal!277

ENDINGS

See merge request STJr/SRB2Internal!264

Boss enable linedef (type 449)

See merge request STJr/SRB2Internal!272

Snap to ground fix

Closes #165

See merge request STJr/SRB2Internal!274

MP/Old Special Stage ring stuff

See merge request STJr/SRB2Internal!276

New award rings linedef executor

See merge request STJr/SRB2Internal!263

Fix old Special Stage failure sounds not always playing

See merge request STJr/SRB2Internal!275

Titlemap Lua

See merge request STJr/SRB2Internal!270

Add rings to old/MP special stage HUD + make both them and spheres (in old special stage only) count down rather than up, to match s3k

Bustables and landing events

Closes #157 and #162

See merge request STJr/SRB2Internal!262

Spring angles and ring angles

See merge request STJr/SRB2Internal!266

Special stage related fixes

See merge request STJr/SRB2Internal!269

MANIASPHERES de-hardcode

See merge request STJr/SRB2Internal!268

Additional spring flags

See merge request STJr/SRB2Internal!256

Smiles tail scale

See merge request STJr/SRB2Internal!273

Diagonal spring ring fixes

See merge request STJr/SRB2Internal!267

Modify P_CheckSector with a modified version of Sal's attempted proper fix for polyobjects crushing, so that we only need to check the polyobject's control sector directly in the waypoints code.

This time I've definitely fixed that teleport to ground issue I'm pretty sure, I don't get it in my tests at least.

Add openfloorrover and openceilingrover vars so that PIT_CheckLine can update tmfloorrover and tmceilingrover properly via P_LineOpening

...which should hopefully stop that issue where you just teleport back to the ground. Assuming this works as expected.

Also this is untested lol.

Instead of checking whether mobj->spawnpoint->extrainfo is in the correct range every tic, have a lua error for trying to set it outside (since there'll no doubt be other consequences to being outside the range too)

Was reviewing old merge requests as a procrastination technique, and discovered that the followmobj's scale was being inaccurately handled for Smiles' tails! Fixed that...

	- Frontside x offset = boss ID (determined via parameter for all bosses)
	- Noclimb flag = disable mode
	- Bosses don't do a fuckin' THING - no state updates, no player searches, no sounds, no lua, no nothin' - and it's all totally netsynced.
	- The only thing they WILL do is flash infinitely if you hurt them, but this is designed for stuff where you're not meant to be in the same room as the boss til it's activated.
	- All bosses of all IDs are automatically enabled on mapload, then if an enable mode version of this linedef is present in the map for a specific boss id, that boss id is automatically disabled.
* Add multi-boss support via parameter for:
	- All bosses' MT_BOSSFLYPOINT search
	- Boss 5's waypoint search
	- Oldbrak's waypoint search (this one's for you, jood)

# Conflicts:
#	src/p_user.c

* Strip the word "function" from INLEVEL error messages, since they're now shared between access and function cases.
* Move it into lua_script.h, so it's available to everything that needs it.

Fix lua scripts erroring on the title screen because they're run there but it's not counted as GS_LEVEL (aka #168).

* Fix something I neglected earlier when fixing Ghosts and Replays for 2.2 - the fact that the player's skin will change if they don't have NiGHTS sprites like Sonic does not being accomodated.