Declare some DEFVARs globally, not locally

Declare some DEFVARs globally, not locally

	* gtkutil.h (x_gtk_use_old_file_dialog, x_gtk_show_hidden_files)
	(x_gtk_file_dialog_help_text, x_gtk_whole_detached_tool_bar):
	Declare.
	* gtkutil.c (xg_uses_old_file_dialog):
	(xg_get_file_with_chooser):
	(xg_tool_bar_detach_callback): Don't redeclare globals.