Also features jittering of the intermission elements because I thought it'd be fun, plus some better handling of players leaving (and then new ones joining) mid-intermission.
* Make MT_GHOST's encoremapping depend on whether the source was encoremapped.
* Revamp how sector typegroup 2, type 15 inverts the encoremapping (so planes don't get awkwardly desynchronised).
* V_DrawFixedPatch and ilk:
* Change the offset of V_FLIP so it's not one screen-pixel off where its non-flipped sprite would have started being drawn from.
* Write to x and y as well as desttop so that anti-screen-overflow checks later in the function behave properly with non-green resolutions.
* V_DrawFill:
* Reduce number of operations performed upon `c`.
* V_DrawString and ilk:
* Offset the left and right boundary checks in non-green resolutions such that you can actually draw stuff to the left of basevid screen x coordinate 0.
* Stop orphaning their memory. They ARE PU_LEVEL, so they'll disappear eventually, but, like... it's not good memory management practice to just *orphan* them when you're literally never going to do anything with them ever again. Y'know?
* Make ghosts spawn properly on slopes.
* 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...
