Prefer GLX over EGL
Prefer GLX over EGL

fixes #314 for me.

I've "tested" change by running examples (which prior to change simply
crashed), but since I did not run those examples successfuly ever before,
I don't know whether they worked as intended.

ecoal95/glutin,mbrubeck/glutin,mneumann/glutin,mmatyas/glutin,servo/glutin,Jayflux/glutin,nc4rrillo/glutin,tempbottle/glutin,mitchmindtree/glutin,vberger/glutin,kornholi/glutin,nox/glutin,fkaa/glutin,TimNN/glutin,mbrubeck/glutin,vvuk/glutin,Ms2ger/glutin,notriddle/glutin,bvssvni/glutin,tomaka/winit,adambadawy/glutin,tomaka/glutin,mvdnes/glutin,retep998/glutin,ozkriff/glutin