pgsql: Represent BETWEEN as a special node type in raw parse trees.

Represent BETWEEN as a special node type in raw parse trees.

Previously, gram.y itself converted BETWEEN into AND (or AND/OR) nests of
expression comparisons.  This was always as bogus as could be, but fixing
it hasn't risen to the top of the to-do list.  The present patch invents an
A_Expr representation for BETWEEN expressions, and does the expansion to
comparison trees in parse_expr.c which is at least a slightly saner place
to be doing semantic conversions.  There should be no change in the post-
parse-analysis results.

This does nothing for the semantic issues with BETWEEN (dubious connection
to btree-opclass semantics, and multiple evaluation of possibly volatile
subexpressions) ... but it's a necessary preliminary step before we could
fix any of that.  The main immediate benefit is that preserving BETWEEN as
an identifiable raw-parse-tree construct will enable better error messages.

While at it, fix the code so that multiply-referenced subexpressions are
physically duplicated before being passed through transformExpr().  This
gets rid of one of the principal reasons why transformExpr() has
historically had to allow already-processed input.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/34af082f95aa6adb8af5fbd4da46bd4c3c176856

Modified Files
--------------
src/backend/nodes/outfuncs.c    |   16 ++++++
src/backend/parser/gram.y       |   56 ++++++++-------------
src/backend/parser/parse_expr.c |  102 +++++++++++++++++++++++++++++++++++++++
src/include/nodes/parsenodes.h  |    6 ++-
4 files changed, 144 insertions(+), 36 deletions(-)