[Ohrrpgce] SVN: teeemcee/8621 gfx_sdl: Add mouse wheel up/down as mouse buttons.

[subversion at HamsterRepublic.com]

teeemcee
2017-04-08 16:12:25 -0700 (Sat, 08 Apr 2017)
222
gfx_sdl: Add mouse wheel up/down as mouse buttons.

Also allow checking these buttons using "mouse button" and "mouse click",
but it's undocumented, because other backends don't support it yet.
Added a test to collider.rpg
---
U   wip/gfx_sdl.bas
U   wip/scancodes.bi
U   wip/scriptcommands.bas
U   wip/testgame/collider.hss
U   wip/testgame/collider.rpg