Remove extra magnitude from magic texture mapping values

- These used to be fixed point, but now they're floating point, so the
  excess magnitude is unneeded.
Remove DepthScale and DepthOrg from FWallTmapVals
- Moved bot specific functions into DBot.
Merge branch 'BotFunctions' of https://github.com/ChillyDoom/zdoom
Destroy mod-created CVars when 'restart' is invoked
Fixed weapon drawing rules to account for the death camera [backported from gzdoom], also fixed drawing rules for crosshair
Merge branch 'bug-47011' of https://github.com/kevans91/zdoom
Fixed SV_SAMESPAWNSPOT behavior -- When enabled, use the p->mo->z. Otherwise, rely on ONCEILINGZ/FLOATRANDZ/ONFLOORZ w/ or w/o UsePlayerStartZ as previously done
- fixed: All powerup blend colors with an alpha of 0 were treated as 'has no color' for PowerupGivers.
Make the respawn invulnerability APowerInvulnerable persist through a ClearInventory by making it undroppable
Merge branch 'bug-46152' of https://github.com/kevans91/zdoom
- turned out that the recent change to allow cancelling a powerup blend through a powerup giver did not work well so now there's an explicit 'Powerup.Color none' to do it that works a bit differently.
- fixed: ZDoom did not understand Boom's name for the Red Skull Key pickup message due to a typo.

Of course, just changing the name would break many old ZDoom mods so now Boom's name is explicitly being translated into ZDoom's before setting the string.
- gcc warnings suck...
- missed a return.
- Ported SDL backend to SDL 2.0. Still needs a little bit of polish, but it works.
- Enabled vid_vsync for SDL2 although just turning it on doesn't perform right.
- Improved fullscreen a bit.
- Splitting the pull request in half.
- Added THRUREFLECT, MIRRORREFLECT, and AIMREFLECT. All require REFLECTIVE to work.
- THRUREFLECT prevents missiles from changing course if reflected, and takes precedence over all reflective flags.
- MIRRORREFLECT causes missiles to perform a direct 180 turn-around.
- AIMREFLECT turns the missile back to the original shooter, and does not slow the missile down.
- Added three missile impact pointer changing flags.
- HITTARGET, HITMASTER, and HITTRACER.
- A missile that dies hitting an actor will set this impacted actor as the new target/master/tracer, depending on specifications.
- Removed XCursor code since SDL2 has proper color cursor support.
- Improved international keyboard support by falling back to scan codes if we don't recognize a keycode.
- Clear out any residual mouse movement when entering relative mouse mode.