GFZ boss rework + boss explosion fun

See merge request STJr/SRB2Internal!290

Added quick validity checks for three linedef executor specials that require a player mobj to be the triggerer (432, 434 and 437)

MI cleanup returns

See merge request STJr/SRB2Internal!292

Fix all our landing woes. (For now.)

See merge request STJr/SRB2Internal!289

# Conflicts:
#	src/config.h.in
#	src/d_clisrv.c
#	src/d_netcmd.c
#	src/doomdef.h
#	src/p_map.c
#	src/p_maputl.c
#	src/sdl12/macosx/Srb2mac.xcodeproj/project.pbxproj

Update version to 2.1.25

See merge request STJr/SRB2!507

Fix an exploit where players could steal the final hash of a login

See merge request STJr/SRB2!508

PolyObject crush hotfix

See merge request STJr/SRB2!506

Use P_MobjInsidePolyobj instead of P_MobjTouchingPolyobj, so that you can be crushed by the polyobject's middle rather than just its edges

PolyObject fixes backport

See merge request STJr/SRB2!505

# Conflicts:
#	src/p_user.c

After looking at the FOF part of P_LineOpening for a while I now realise many of these variables aren't even necessary, so I removed them all.

(Naturally I did the same to the camera equivalent)

# Conflicts:
#	src/p_maputl.c

Edit a lot of the rest of the polyobject-related code in P_LineOpening to make more sense and be more optimised.

* If you collide with a line belonging to a polyobject, you should NEVER have to care about any FOFs that might be present in either sector of the linedef. This could lead to colliding with ghostly FOFs that aren't actually there or something dumb, if someone decided to give either of the polyobject's control sectors FOFs for some reason. We don't want that, obviously.
* Polyobjects without POF_CLIPPLANE apparently are supposed to have a top and bottom "physical" height of value INT32_MAX and _MIN respectively, according to P_CheckPosition ...let's be consistent with this.
* Finally, there is no more need for that back = front nonsense hack anymore with my changes made.

# Conflicts:
#	src/p_maputl.c

P_LineOpening: set int32 max/min as defaults for opentop, openbottom etc if a linedef you touched belongs to a polyobjetc. the only thing that really matters in this scenario is the polyobject itself after all!

# Conflicts:
#	src/p_maputl.c

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.

Tweak the Metal Sonic death explosion sequence. It's longer than all the others before the egg capsule comes up, but so is Mecha Sonic in s3k, so it fits.

(Not uploading an exe for this miniscule change. If you want to play with this, get it in Master. :P )

Tweak the ACZ3 fight a little, animationwise, since every other non-Brak boss got an upgrade to its death anim in this branch.

Also make its bomb throw anim use all the new sprites.

Initialise player_names[] in D_RegisterClientCommands such that we don't need to have to manually update it if MAXPLAYERS ever changed

Since I had to do a clean build to get this up to date (the state list was updated), I decided to redo all the boss explosion animations to be way more aesthetically pleasing.

Basically, think "Sonic 3". https://cdn.discordapp.com/attachments/371082353990303745/610233312765673493/srb20047.gif