small makeVar refactoring

Peter Eisentraut <peter_e@gmx.net> writes:

While hacking around, I noticed that a lot of makeVar() calls could be
refactored into some convenience functions, to save some redundancy and
so that the unusual call patterns stand out better. Useful?

I'm not real thrilled with importing catalog/pg_attribute.h into
makefuncs.h; that seems like a lot of namespace pollution for not much
return. So -1 to makeVarFromAttribute. The other is okay although I'm
not convinced it's useful enough to bother with.

regards, tom lane