First phase of plan-invalidation project: create a plan cache management

module and teach PREPARE and protocol-level prepared statements to use it.
In service of this, rearrange utility-statement processing so that parse
analysis does not assume table schemas can't change before execution for
utility statements (necessary because we don't attempt to re-acquire locks
for utility statements when reusing a stored plan).  This requires some
refactoring of the ProcessUtility API, but it ends up cleaner anyway,
for instance we can get rid of the QueryContext global.

Still to do: fix up SPI and related code to use the plan cache; I'm tempted to
try to make SQL functions use it too.  Also, there are at least some aspects
of system state that we want to ensure remain the same during a replan as in
the original processing; search_path certainly ought to behave that way for
instance, and perhaps there are others.

src/backend/commands/tablespace.c

@@ -37,7 +37,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/tablespace.c,v 1.43 2007/03/06 02:06:13 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/tablespace.c,v 1.44 2007/03/13 00:33:40 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -198,11 +198,6 @@ CreateTableSpace(CreateTableSpaceStmt *stmt)
 	char	   *linkloc;
 	Oid			ownerId;
 
-	/* validate */
-
-	/* don't call this in a transaction block */
-	PreventTransactionChain((void *) stmt, "CREATE TABLESPACE");
-
 	/* Must be super user */
 	if (!superuser())
 		ereport(ERROR,
@@ -385,9 +380,6 @@ DropTableSpace(DropTableSpaceStmt *stmt)
 	ScanKeyData entry[1];
 	Oid			tablespaceoid;
 
-	/* don't call this in a transaction block */
-	PreventTransactionChain((void *) stmt, "DROP TABLESPACE");
-
 	/*
 	 * Find the target tuple
 	 */