Documentation fixups. 
Documentation fixups. 

In particular, move the signal comments to gtkosxapplication_quartz.c, where Gtk-doc seems to like them better,
GNOME/gtk-mac-integration,sharoonthomas/gtk-mac-integration,sharoonthomas/gtk-mac-integration,GNOME/gtk-mac-integration,sharoonthomas/gtk-mac-integration,jralls/gtk-mac-integration,jralls/gtk-mac-integration,sharoonthomas/gtk-mac-integration,sharoonthomas/gtk-mac-integration,jralls/gtk-mac-integration,GNOME/gtk-mac-integration