Gdk::Pixbuf: Deprecate create_from_inline()

* gdk/src/pixbuf.hg: Deprecate create_from_inline() because
gdk_pixbuf_new_from_inline() is deprecated in gdk-pixbuf.
Gtk::SearchEntry: Wrap the search-changed signal

* gtk/src/searchentry.hg: Wrap the search-changed signal.
Gtk::Dialog: Add constructors with DialogFlags

* gtk/src/dialog.[hg|ccg]: Wrap enum GtkDialogFlags. Add constructors that
wrap gtk_dialog_new_with_buttons() and take a Gtk::DialogFlags parameter.
A dialog can then be created with a header bar. Bug #738513.