Lighting fixes? Plane and simple!

See merge request !268

Introduce a temporary measure to enable the old stuff, minus one of the most obviously terrible bugbears of yesteryear. Let it be known that any downstream poirt will almost certainly toggle this ASAP.

* Fix that thing where ALL transparent FOF planes were continuously fullbright unless encased in a fog which disables sprite fullbrightness, which was long-hated by many people in the community!
	* For backwards compatibility, setting flag 1 in that fog field (which is probably the most common "in-the-wild" usage of this feature) will continue to make objects un-fullbright.
	* For situations where you desperately want the behaviour to be enabled, you can apply fog flag 2.
* Change the fadestart and fadeend range in which colormaps are generated.
	* The problem HERE was that the darkest light level reached by generated colormaps was actually slightly brighter than the darkest level reached by normal colormaps.
	* The typo I fixed does have SOME basis in fact - standard colormap lumps are 34 (33 in 0-indexing) long rather than 32 (31), but whoever wrote this didn't realise that the code for generating them didn't do it DooM style, just bright-to-dark with no extras on the end...

update XPM icon

See merge request !267

Change default sound volume

See merge request !238

SDL Mixer fixes

Closes #31

See merge request !260

Fix white being treated as transparent.

See merge request !266

Woops! All trans

See merge request !265

Transparency? I hardly knew 'er!

See merge request !264

Change the order of operations when applying transparency and colormap such that colormap isn't applied to the screen pixel twice (or, in the case of R_DrawTranslatedTranslucentColumn_8, thrice).

Please note I haven't touched the ASM equivalent, given as it's not actually used.

Password fix hotfix

See merge request !261

Quick fix for LJ's password fix: don't check if password is set until we've confirmed that the receiving player is the server!

GME low volume fix

See merge request !248

Fix pausing on gme

See merge request !251

This should prevent I_FreeSfx making a mess of things later, hopefully.

OpenGL: FOF walls + Lower unpegged

See merge request !258

OpenGL HWR_ProjectSprite fix

See merge request !255

More helpful error messages

See merge request !243

Smoother MD2 interpolation

See merge request STJr/SRB2!224

Fixed MD2 models not loading correctly on Linux

Lua exploit fix

See merge request !259

Disable admin password by default

Minor net command fixes