FTP Protocol extensions permit the use of a special "EPSV" command.

	NATs may be able to put the connection on a "fast path" through the
	translator using EPSV, as the EPRT command will never be used
	and therefore, translation of the data portion of the segments 
	will never be needed.

	Turning this OFF will prevent EPSV being attempted.
	WARNING: Doing so will convert Squid back to the old behavior with all
	the related problems with external NAT devices/layers.

	Requires ftp_passive to be ON (default) for any effect.