Re: Improvements in psql hooks for variables

   I wrote:

> So I went through the psql commands which don't fail on parse errors
> for booleans
> [...]

Here's a v5 patch implementing the suggestions mentioned upthread:
all meta-commands calling ParseVariableBool() now fail
when the boolean argument can't be parsed successfully.

Also includes a minor change to SetVariableAssignHook() that now
returns the result of the hook it calls after installing it.
It doesn't make any difference in psql behavior since callers
of SetVariableAssignHook() ignore its return value, but it's
more consistent with SetVariable().