Avoid recursion when processing simple lists of AND'ed or OR'ed clauses.

Since most of the system thinks AND and OR are N-argument expressions
anyway, let's have the grammar generate a representation of that form when
dealing with input like "x AND y AND z AND ...", rather than generating
a deeply-nested binary tree that just has to be flattened later by the
planner.  This avoids stack overflow in parse analysis when dealing with
queries having more than a few thousand such clauses; and in any case it
removes some rather unsightly inconsistencies, since some parts of parse
analysis were generating N-argument ANDs/ORs already.

It's still possible to get a stack overflow with weirdly parenthesized
input, such as "x AND (y AND (z AND ( ... )))", but such cases are not
mainstream usage.  The maximum depth of parenthesization is already
limited by Bison's stack in such cases, anyway, so that the limit is
probably fairly platform-independent.

Patch originally by Gurjeet Singh, heavily revised by me

contrib/postgres_fdw/deparse.c

@@ -1716,9 +1716,6 @@ deparseRelabelType(RelabelType *node, deparse_expr_cxt *context)
 
 /*
  * Deparse a BoolExpr node.
- *
- * Note: by the time we get here, AND and OR expressions have been flattened
- * into N-argument form, so we'd better be prepared to deal with that.
  */
 static void
 deparseBoolExpr(BoolExpr *node, deparse_expr_cxt *context)