Clean up the mess around EXPLAIN and materialized views.

Revert the matview-related changes in explain.c's API, as per recent
complaint from Robert Haas.  The reason for these appears to have been
principally some ill-considered choices around having intorel_startup do
what ought to be parse-time checking, plus a poor arrangement for passing
it the view parsetree it needs to store into pg_rewrite when creating a
materialized view.  Do the latter by having parse analysis stick a copy
into the IntoClause, instead of doing it at runtime.  (On the whole,
I seriously question the choice to represent CREATE MATERIALIZED VIEW as a
variant of SELECT INTO/CREATE TABLE AS, because that means injecting even
more complexity into what was already a horrid legacy kluge.  However,
I didn't go so far as to rethink that choice ... yet.)

I also moved several error checks into matview parse analysis, and
made the check for external Params in a matview more accurate.

In passing, clean things up a bit more around interpretOidsOption(),
and fix things so that we can use that to force no-oids for views,
sequences, etc, thereby eliminating the need to cons up "oids = false"
options when creating them.

catversion bump due to change in IntoClause.  (I wonder though if we
really need readfuncs/outfuncs support for IntoClause anymore.)

src/backend/parser/parse_relation.c

@@ -48,6 +48,7 @@ static void expandTupleDesc(TupleDesc tupdesc, Alias *eref,
 				int location, bool include_dropped,
 				List **colnames, List **colvars);
 static int	specialAttNum(const char *attname);
+static bool isQueryUsingTempRelation_walker(Node *node, void *context);
 
 
 /*
@@ -2615,3 +2616,51 @@ errorMissingColumn(ParseState *pstate,
 						   colname, rte->eref->aliasname) : 0,
 			 parser_errposition(pstate, location)));
 }
+
+
+/*
+ * Examine a fully-parsed query, and return TRUE iff any relation underlying
+ * the query is a temporary relation (table, view, or materialized view).
+ */
+bool
+isQueryUsingTempRelation(Query *query)
+{
+	return isQueryUsingTempRelation_walker((Node *) query, NULL);
+}
+
+static bool
+isQueryUsingTempRelation_walker(Node *node, void *context)
+{
+	if (node == NULL)
+		return false;
+
+	if (IsA(node, Query))
+	{
+		Query	   *query = (Query *) node;
+		ListCell   *rtable;
+
+		foreach(rtable, query->rtable)
+		{
+			RangeTblEntry *rte = lfirst(rtable);
+
+			if (rte->rtekind == RTE_RELATION)
+			{
+				Relation	rel = heap_open(rte->relid, AccessShareLock);
+				char		relpersistence = rel->rd_rel->relpersistence;
+
+				heap_close(rel, AccessShareLock);
+				if (relpersistence == RELPERSISTENCE_TEMP)
+					return true;
+			}
+		}
+
+		return query_tree_walker(query,
+								 isQueryUsingTempRelation_walker,
+								 context,
+								 QTW_IGNORE_JOINALIASES);
+	}
+
+	return expression_tree_walker(node,
+								  isQueryUsingTempRelation_walker,
+								  context);
+}