When updating a single entry (i.e. when the `-u' option is given),

When updating a single entry (i.e. when the `-u' option is given),
do not add the "\xFF" "VERSION" key --- it should only be added once
ALL entries have been updated.

While I'm here, correct the logic that detects whether or not the
user-ID has changed so that it works even if all entries have not
yet been updated to the new format.

Users missing-in-action were
Reported by:	tjr, Vallo Kallaste <vallo@estcard.ee>,
		    leafy <leafy@leafy.idv.tw>

Sponsored by:	DARPA, Network Associates Laboratories