Factor out function to discard the loading process and the current folder file

Factor out function to discard the loading process and the current folder file
	(discard_loading_and_current_folder_file): Factor out function to
	cancel the cancellable and discard the current_folder_file,
	i.e. to reset the invariant to the "nothing valid is loaded" case.
	(gtk_file_chooser_entry_dispose): Use
	discard_loading_and_current_folder_file().
	(reload_current_folder): Likewise.
	(refresh_current_folder_and_file_part): Likewise, and ensure that
	the error cases result in the invariant being held.

Signed-off-by: Federico Mena Quintero <federico@novell.com>
svn path=/trunk/; revision=22181