actually a type-coercion problem.  If you have a function defined on
class A, and class B inherits from A, then the function ought to work
on class B as well --- but coerce_type didn't know that.  Now it does.

  * Portions Copyright (c) 1996-2000, PostgreSQL, Inc

to all files copyright Regents of Berkeley.  Man, that's a lot of files.

yet, but at least we can give a better error message:
regression=> select count(distinct f1) from int4_tbl;
ERROR:  aggregate(DISTINCT ...) is not implemented yet
instead of 'parser: parse error at or near distinct'.

sort order down into planner, instead of handling it only at the very top
level of the planner.  This fixes many things.  An explicit sort is now
avoided if there is a cheaper alternative (typically an indexscan) not
only for ORDER BY, but also for the internal sort of GROUP BY.  It works
even when there is no other reason (such as a WHERE condition) to consider
the indexscan.  It works for indexes on functions.  It works for indexes
on functions, backwards.  It's just so cool...

CAUTION: I have changed the representation of SortClause nodes, therefore
THIS UPDATE BREAKS STORED RULES.  You will need to initdb.

used to overrun its fixed-size arrays before detecting error; not cool).
Also, replace uses of magic constant '8' with 'MAXFARGS'.