Fix bug 6286 (get 3 directory loads instead of 1 when you activate
	file in directory view [as opposed to typing location]). This is
	mostly right, but there's still a relatively common case where we
	get a 2nd directory load. I'll have to write a bug report about
	that case, but it's no worse than before and quite a bit better.

	* src/file-manager/fm-directory-view.c:
	(fm_directory_view_destroy): Stop monitoring. Also change the old
	monitoring code to use different "client" pointers so multiple
	monitors don't interfere with each other.
	(activate_callback): Stop monitoring when we get to the point of
	actually activating (unless we are opening through the shell).
	Also do some small cleanup to "command:" handling code and fix
	minor storage leak.
	(cancel_activate_callback): Stop monitoring if we cancel.
	(fm_directory_view_activate_file): Start monitoring so the load
	can be shared between all who need it. This is the same
	optimization done at the shell...