Change mixer panning to make sense

This makes positional audio in sdl work correctly (things to the left
play sounds in the left speaker)
Merge remote-tracking branch 'Furyhunter/sdl-fix-flippedchannels'
 Change mixer panning to make sense (for SDL12)

    This makes positional audio in sdl work correctly (things to the left
    play sounds in the left speaker)
Remove momentum reduction in CA_JUMPTHOK

Also add new multiability handling for it
SRB2 2.1.10 release
Merge branch 'next'
Merge branch 'master' into next
Merge pull request #28 from wolfy852/master

Remove momentum reduction in CA_JUMPTHOK
SRB2 2.1.11 release
Merge branch 'next'
evil changes
Workaround gcc 4.7 ABI incompat

-mno-ms-bitfields causes 2-byte offset in net packets on mingw builds.
Builds with gcc 4.7+ should now support multiplayer.
Use gcc_struct on ATTRPACK too
SDL2: Fix 320x200 mode
SDL2: Reimplement some stubbed commands

Also remove some unnecessary functions.
SDL2: Do not use xinput, force directinput

Fixes axes issue with xinput controllers.
SDL2: Add 1600x1200 mode
Merge branch 'master' into uncapped
uncapped: add cap framerate option in menu