gcc has optimizations for include guards that only work if they are outermost in the the header. https://bugzilla.gnome.org/show_bug.cgi?id=689810
This patch changes all uses of GDK_DEPRECATED(_FOR) in gtk headers by the versioned variants, GDK_DEPRECATED_IN_3_x(_FOR). At the same time, we add GDK_AVAILABLE_IN_3_x annotations for all API additions in 3.2 and 3.4.
Also install their headers to a subdirectory.
