Re: Improvements in psql hooks for variables

BTW, while testing this patch I noticed that the error reports are
a tad redundant:

regression=# \set AUTOCOMMIT foo
unrecognized value "foo" for "AUTOCOMMIT": boolean expected
\set: error while setting variable
regression=# 

The "error while setting variable" message seems entirely content-free.
I think we should drop that and instead establish a rule that SetVariable
should print a message for itself about any failure.  (There are a lot
of call sites that don't check for or print a message, but that's only
because they aren't expecting failure.  If one were to happen, printing
a message doesn't seem unreasonable.)  That would in turn propagate into
an API requirement that var hooks that return FALSE are responsible for
printing a message about the reason, which is why it would be appropriate
to make that change as part of this patch.

Barring objections PDQ, I'll make this change.

			regards, tom lane