glib-2.0: make VariantDict.end return a floating reference
glib-2.0: make VariantDict.end return a floating reference

The underlying implementation returns a floating reference. Reflecting
this in the vapi silences the warning about g_variant_unref called once
too many.

Fixes bug 734611

flobrosch/vala-fixes,spidermonkdust/vala,flobrosch/vala-fixes,rvu95/vala,GNOME/vala,frida/vala,GNOME/vala,frida/vala,spidermonkdust/vala,GNOME/vala,rvu95/vala,frida/vala,flobrosch/vala-fixes,rvu95/vala,GNOME/vala,frida/vala,spidermonkdust/vala,frida/vala