ietf-nntp "Common NNTP Extensions" document updated

[Dave Barr]

The section on XREPLIC should have the following paragraph appended.

	XREPLIC slaving is being deprecated in the current version of INN.
	INN now has the ability to slave servers via transparent means, simply
	by having the article's Xref header transferred.  (previously this
	header was generated locally and stripped off on outgoing feeds).
	It is likely that future versions of INN will no longer support
	XREPLIC.

--Dave