Fix ref_sink of Gtk.Window created with GLib.Object.new
Fix ref_sink of Gtk.Window created with GLib.Object.new

Fixes bug 618750.

playya/vala,spidermonkdust/vala,Distrotech/vala,frida/vala,tjol/vala-tjol,rvu95/vala,frida/vala,kamanashisroy/aroop,tjol/vala-tjol,playya/vala,playya/vala,GNOME/vala,jessevdk/vala,Distrotech/vala,xdave/pvala,rvu95/vala,jessevdk/vala,frida/vala,spidermonkdust/vala,tjol/vala-tjol,kamanashisroy/aroop,severinh/vala,severinh/vala,flobrosch/vala-fixes,spidermonkdust/vala,frida/vala,Distrotech/vala,frida/vala,GNOME/vala,kamanashisroy/aroop,GNOME/vala,flobrosch/vala-fixes,severinh/vala,rvu95/vala,flobrosch/vala-fixes,jessevdk/vala,GNOME/vala