Set close-on-exec for download channels
Set close-on-exec for download channels

Seems to stop Windows seeing the download file as empty after closing
it, though I don't know why.

bartbes/0install,pombreda/0install,bastianeicher/0install,bhilton/0install,gfxmonk/0install,0install/0install,bastianeicher/0install,bhilton/0install,bartbes/0install,jaychoo/0install,gasche/0install,DarkGreising/0install,bartbes/0install,DarkGreising/0install,pombreda/0install,0install/0install,pombreda/0install,DarkGreising/0install,gasche/0install,bhilton/0install,jaychoo/0install,jaychoo/0install,HoMeCracKeR/0install,gfxmonk/0install,HoMeCracKeR/0install,gasche/0install,gfxmonk/0install,HoMeCracKeR/0install,bastianeicher/0install,gasche/0install,0install/0install