Rename xfce_execute to xfce_spawn. I've also renamed both
functions to match Glib/Gdk.

Remove xfce_gdk_pixbuf_new_from_inline_at_size and
xfce_gtk_dialog_parse_parent.

Use GtkWindows's for the parents of the dialogs.

Add support for secondary text in the info, warnings
and questions dialog functions.

Rename the internal function xfce_message_dialog_vnew to
xfce_message_dialog_new_valist.


(Old svn revision: 30214)