of the SELECT part of the statement is just like a plain SELECT.  All
INSERT-specific processing happens after the SELECT parsing is done.
This eliminates many problems, e.g. INSERT ... SELECT ... GROUP BY using
the wrong column labels.  Ensure that DEFAULT clauses are coerced to
the target column type, whether or not stored clause produces the right
type.  Substantial cleanup of parser's array support.

sure if they are all fixed, because rewriter is now the stumbling block,
but at least some cases work that did not work before.

will gradually replace all of the boilerplate tree-walk-recursion code that
currently exists in O(N) slightly different forms in N subroutines.
I've had it with adding missing cases to these subroutines...

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