Split off gtkprivate.h

The gtkprivate.h header contains GtkWidget-specific private symbols that
are not useful except in a handful of cases. Basically everything
includes gtkprivate.h for the GTK_PARAM_* macros.

https://bugzilla.gnome.org/show_bug.cgi?id=632539

gtk/gtkrecentmanager.c

@@ -103,6 +103,7 @@
 
 #include "gtkrecentmanager.h"
 #include "gtkintl.h"
+#include "gtksettings.h"
 #include "gtkstock.h"
 #include "gtkicontheme.h"
 #include "gtktypebuiltins.h"