Revert of the FF_MIDDLESTARTCHANCE changes for player states, although the flag still exists internally since there's no reason to remove it.

# Conflicts:
#	src/d_player.h
#	src/dehacked.c
#	src/info.c
#	src/p_user.c

Sideways springs, horizontal hog-launchers, perpendicular plungers...

Call them what you like, they're in the code now. And have been for months!

Nev3r uses the hell out of these and I'm fed up of them being <!>'s all over the place, so please have 'em in master so we can update srb2.srb and make things better for all of us.

See merge request !30

Cleanup of P_CheckUnderwaterAndSpaceTimer's conditional checks for future PF_ROBOT changes, where characters like Metal make electric zaps instead of bubbles.

Dashmode

This branch Metal Sonic's abilities (CA_DASHMODE) to the game.

See merge request !26

Ported CA_HAMMER from new-character-actions in a way that takes advantage of all of the non-hardcodey things I've added in this branch.

Also, it's called CA_TWINSPIN because that's more inoccouous.

On MI's reccomendation, a skin flag to disable the effects of FF_MIDDLESTARTCHANCE for specific characters whose animations might not be symmetrical.

* FF_MIDDLESTARTCHANCE - has a 50% chance of starting the spr2 or FF_ANIMATE animation halfway in
* FF_SPR2ENDSTATE - if var1 == S_NULL, don't loop, just stop incrementing the frames. Otherwise, go to the state represented by var1.

The former is just something I did for fun, the latter is something that'll come in handy when porting in new-character-moves.

Realised the potential for out-of-bounds memory accessing, so put some limits in place to prevent that from happening.

(skin->availability is a UINT8, so it'll never be negative)

Setup:
* S_SKIN needs an "availability" line. Set to 0 to have always available, otherwise is assumed to be UINT8 unlockable number. If it's a valid unlockable, its name will be copied over with the character's realname.
* Define an unlockable via SOC or hardcode. If you don't want it visible on the Secrets menu, just set its type to None. Everything else is as normal - you can set the conditionset to whatever, objective, height, nochecklist, nocecho...

Also, new default for revitem to match player.dta, and an updated Force Skin netgame option name to reflect the fact it's string based now.

Meanwhile, a sneaky sneaky for hiding hidden characters further.

Also, I guess CA_SWIM isn't forced into running on water anymore.

* radius - sets the player's radius for that skin.
* height - sets the player's normal height for that skin.
* spinheight - sets the player's spinheight for that skin.
* shieldscale - see http://i.imgur.com/BQ5DhKC.png for justification

Rudimentary SOC shuffling if you add a character with the same name as a previous character to prevent character select from breaking.

More clearly defined handling for replacing character select images. Specifically takes into account whether the hidden character was added in this file or a seperate one.

Also, removed some commented out code regarding character selects, and removed a useless case for R_SkinAvailable().

* support hidden characters
* take the skin->name, not the number
* display the skin->name in the menu

Also, minor tweaks to other things.

R_SkinUnlock defines the circumstances under which a skin is available. For simplicty's sake, I've currently bound it to an S_SKIN variable so I can toggle it easily, but it WILL be replaced with a hook into the savegame system at some point.
* Currently has three tiers of unlock - freebie (forceskin or modeattacking via a loaded replay), Ringslinger Only, and SP/Coop and Ringslinger.
* I don't know anything about netcode so I basically decided to make R_SkinUnlock relevant only under local circumstances, try as hard as possible to stop bad skin info from getting sent to the server, and then admit defeat once the server has the information. If this is a bad choice, please discipline me and show me how to fix it.
* Character Select now checks for whether the character is hidden or not on menu load and does/undoes it based on that info, but will never touch one disabled via SOC. I also used this opportunity to optimise, checking for/filling out charsel pictures instead of doing it later. (It now also includes special casing for a select screen with zero characters!)
* Mode Attack now hides hidden characters in its character select based on SP rules.

Things that still need to be done:
* ForceSkin_OnChange. Is there a graceful way to handle this?
* No obvious skin name conflicts. Add a salt to the names of hidden skins, and then remove it when they're unhidden?
* The gap between Knuckles' skin number and the first custom character anybody adds will be way too obvious. A seperate hidden skin numbering system? Start at 32 and count up from there? There's a few ways...

Also, bugfix for something my optimisation introduced.

* If a character select character image is not set, don't iterate every tic - iterate on first image get and then save to the struct.
* A character select screen with only two characters now has special case handling.
* A memory leak in the making has been plugged. (specifically, picname not being Z_Free'd if the loop fails to do so)
* Logic/operation simplification.

Also, some typo corrections and clarity case movements of stuff in other files I've been looking at.

For GCC 6.1 builds

I do not know what I was doing:

NULL checks

building without BLUA support

functions that do not depend on outside vars should be tagged with "const", AKA, FUNCMATH

See merge request !89