Use the 0.8.x line of libasync.
Use the 0.8.x line of libasync.

Conflicts:
	core/dub.sdl

etcimon/vibe.d,chalucha/vibe.d,etcimon/vibe.d,rejectedsoftware/vibe.d,Geod24/vibe.d,gedaiu/vibe.d,DBankov/vibe.d