Separate parse-analysis for utility commands out of parser/analyze.c

(which now deals only in optimizable statements), and put that code
into a new file parser/parse_utilcmd.c.  This helps clarify and enforce
the design rule that utility statements shouldn't be processed during
the regular parse analysis phase; all interpretation of their meaning
should happen after they are given to ProcessUtility to execute.
(We need this because we don't retain any locks for a utility statement
that's in a plan cache, nor have any way to detect that it's stale.)

We are also able to simplify the API for parse_analyze() and related
routines, because they will now always return exactly one Query structure.

In passing, fix bug #3403 concerning trying to add a serial column to
an existing temp table (this is largely Heikki's work, but we needed
all that restructuring to make it safe).

src/include/parser/parse_node.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/parser/parse_node.h,v 1.51 2007/01/05 22:19:57 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/parser/parse_node.h,v 1.52 2007/06/23 22:12:52 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -83,6 +83,7 @@ typedef struct ParseState
 } ParseState;
 
 extern ParseState *make_parsestate(ParseState *parentParseState);
+extern void free_parsestate(ParseState *pstate);
 extern int	parser_errposition(ParseState *pstate, int location);
 
 extern Var *make_var(ParseState *pstate, RangeTblEntry *rte, int attrno);