Duplicate code in psql's \ commands

Folks,

While working on the new improved \df, I noticed a pretty major
infelicity, namely that \ commands get validated by two completely
independent code paths, namely tab-complete.c and
command.c/describe.c.

I'm thinking it would be a good idea to factor the validating out as
far as possible.  This would also make it easier to make sure that tab
completion and \'s output match to the maximal reasonable extent.

Objections?

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

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