New warning code for missing FROM relations

I have committed new warning code to alert users who auto-create
relations without knowing it.

The new code does not throw a warning for:
SELECT pg_language.*;

but does throw one for:
SELECT pg_language.* FROM pg_class

The code issues the warning if it auto-creates a range table entry, and
there is already a range table entry identified as coming from a FROM
clause.  Correlated subqueries should not be a problem because they are
not auto-created.

The regression tests run fine, except for:SELECT *   INTO TABLE tmp1   FROM tmp   WHERE onek.unique1 < 2;NOTICE:
Addingmissing FROM-clause entry for table onekDROP TABLE tmp1;SELECT *   INTO TABLE tmp1   FROM tmp   WHERE
onek2.unique1< 2;NOTICE:  Adding missing FROM-clause entry for table onek2
 

Seems those warnings are justified.  In fact, I am not even sure what
these queries are trying to do.  I have modified the expected files so
they now expect to see the warnings.

A bigger question is whether we should issue ERROR for these queries. 
If they have already used a FROM clause, why would they have other
relations not specified there?

If people have other suggestions about this, I would be glad to modify
the code.  A new function warnAutoRange() does the checking.

--  Bruce Momjian                        |  http://www.op.net/~candle pgman@candle.pha.pa.us               |  (610)
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