Make the mouse wheel events match natural direction on osx.
Make the mouse wheel events match natural direction on osx.

vberger/glutin,Jayflux/glutin,Ms2ger/glutin,mbrubeck/glutin,notriddle/glutin,servo/glutin,pcwalton/glutin,ozkriff/glutin,ecoal95/glutin,adambadawy/glutin,mitchmindtree/glutin,TimNN/glutin,kornholi/glutin,christopheraugustus/glutin,nc4rrillo/glutin,mneumann/glutin,mbrubeck/glutin,mvdnes/glutin,frewsxcv/glutin,retep998/glutin,tomaka/winit,tempbottle/glutin,mmatyas/glutin,robertknight/glutin,larsbergstrom/glutin,bvssvni/glutin,vvuk/glutin,paulrouget/glutin,glennw/glutin,nox/glutin,aepsil0n/glutin,tomaka/glutin,fkaa/glutin