client: handle SpiceMsgMainMigrationBegin (semi-seamless migration)
client: handle SpiceMsgMainMigrationBegin (semi-seamless migration)

RHBZ 725009, 738270
(cherry picked from commit 31ed2519a752b7332ed40d0d7ab02e938c0e65cb branch 0.8)

Conflicts:

	client/red_client.cpp

fgouget/spice,alon/spice-server,mathslinux/spice,freedesktop-unofficial-mirror/spice__spice,elmarco/spice,ya-mouse/spice,SPICE/spice,SPICE/spice,fgouget/spice,ya-mouse/spice,fgouget/spice,Fantu/spice,alon/spice-server,mathslinux/spice,dezelin/spice,alon/spice-server,alon/spice-server,elmarco/spice,Fantu/spice,elmarco/spice,dezelin/spice,ya-mouse/spice,alon/spice-server,freedesktop-unofficial-mirror/spice__spice,freedesktop-unofficial-mirror/spice__spice,mathslinux/spice,SPICE/spice,freedesktop-unofficial-mirror/spice__spice,elmarco/spice,dezelin/spice,dezelin/spice,Fantu/spice,mathslinux/spice,mathslinux/spice,dezelin/spice,freedesktop-unofficial-mirror/spice__spice,elmarco/spice,Fantu/spice,fgouget/spice