glib-2.0: make MainContext.ref_thread_default return value owned
glib-2.0: make MainContext.ref_thread_default return value owned

rvu95/vala,frida/vala,severinh/vala,severinh/vala,GNOME/vala,playya/vala,Distrotech/vala,GNOME/vala,rvu95/vala,spidermonkdust/vala,xdave/pvala,Distrotech/vala,GNOME/vala,GNOME/vala,playya/vala,rvu95/vala,frida/vala,Distrotech/vala,spidermonkdust/vala,flobrosch/vala-fixes,flobrosch/vala-fixes,frida/vala,frida/vala,frida/vala,playya/vala,severinh/vala,flobrosch/vala-fixes,spidermonkdust/vala