Extend EXPLAIN to allow generic options to be specified.

The original syntax made it difficult to add options without making them
into reserved words.  This change parenthesizes the options to avoid that
problem, and makes provision for an explicit (and perhaps non-Boolean)
value for each option.  The original syntax is still supported, but only
for the two original options ANALYZE and VERBOSE.

As a test case, add a COSTS option that can suppress the planner cost
estimates.  This may be useful for including EXPLAIN output in the regression
tests, which are otherwise unable to cope with cross-platform variations in
cost estimates.

Robert Haas

src/include/nodes/parsenodes.h

@@ -13,7 +13,7 @@
  * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/nodes/parsenodes.h,v 1.397 2009/07/20 02:42:28 adunstan Exp $
+ * $PostgreSQL: pgsql/src/include/nodes/parsenodes.h,v 1.398 2009/07/26 23:34:18 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -2193,8 +2193,7 @@ typedef struct ExplainStmt
 {
 	NodeTag		type;
 	Node	   *query;			/* the query (as a raw parse tree) */
-	bool		verbose;		/* print plan info */
-	bool		analyze;		/* get statistics by executing plan */
+	List	   *options;		/* list of DefElem nodes */
 } ExplainStmt;
 
 /* ----------------------