Fix compilation for 32 bit targets
Fix compilation for 32 bit targets

Regression introduced in 47df0e9eaa7f1231a07f86fc44426936c7a2589a

Casting fullscreen_atom (which is the result from XInternAtom, i.e.
c_ulong) as i64 is obviously wrong -- the whole point of types such as
c_ulong is that long in C does *not* always have the same bit size...

Cast it as c_long instead.

While this is the most straightforward fix, I'm not sure it's the best
one: perhaps the x11 crate should offer a set_ulong() method along with
set_long(), which could be used here instead of the cast?

mmatyas/glutin,bvssvni/glutin,notriddle/glutin,nc4rrillo/glutin,mitchmindtree/glutin,kornholi/glutin,vberger/glutin,mbrubeck/glutin,servo/glutin,mbrubeck/glutin,Ms2ger/glutin,ecoal95/glutin,ozkriff/glutin,tomaka/winit,tomaka/glutin