PoC: Make it possible to disallow WHERE-less UPDATE and DELETE

Folks,

Please find attached a patch which makes it possible to disallow
UPDATEs and DELETEs which lack a WHERE clause.  As this changes query
behavior, I've made the new GUCs PGC_SUSET.

What say?

Thanks to Gurjeet Singh for the idea and Andrew Gierth for the tips
implementing.

Best,
David.
--
David Fetter <david(at)fetter(dot)org> http://fetter.org/
Phone: +1 415 235 3778  AIM: dfetter666  Yahoo!: dfetter
Skype: davidfetter      XMPP: david(dot)fetter(at)gmail(dot)com

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