* library/interface.tcl (gdbtk_tcl_file_changed): Handle

	* library/interface.tcl (gdbtk_tcl_file_changed): Handle
	the case of empty-string files, sent by gdb when the
	user requests to reset the file.
	(_close_file): New proc to deal with closing an exe.
	* library/srcbar.itcl (create_file_menu): Add "Close" menu
	option.
	(create_view_menu): Change key binding for Watch Window to
	Ctrl+T to accomodate "Close" going to Ctrl+W.
	* library/srctextwin.itb (config_win): Update key binding
	for Watch Window.
	Add key binding for Close.
	(do_key): Add "close".
	(_clear_cache): Finally implement. I think this works now.