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/include/parser/parse_clause.h

@@ -20,7 +20,7 @@ extern void transformFromClause(ParseState *pstate, List *frmList);
 extern int setTargetTable(ParseState *pstate, RangeVar *relation,
 			   bool inh, bool alsoSource, AclMode requiredPerms);
 extern bool interpretInhOption(InhOption inhOpt);
-extern bool interpretOidsOption(List *defList, char relkind);
+extern bool interpretOidsOption(List *defList, bool allowOids);
 
 extern Node *transformWhereClause(ParseState *pstate, Node *clause,
 					 ParseExprKind exprKind, const char *constructName);

src/include/parser/parse_param.h

@@ -20,5 +20,6 @@ extern void parse_fixed_parameters(ParseState *pstate,
 extern void parse_variable_parameters(ParseState *pstate,
 						  Oid **paramTypes, int *numParams);
 extern void check_variable_parameters(ParseState *pstate, Query *query);
+extern bool query_contains_extern_params(Query *query);
 
 #endif   /* PARSE_PARAM_H */

src/include/parser/parse_relation.h

@@ -96,5 +96,6 @@ extern int	attnameAttNum(Relation rd, const char *attname, bool sysColOK);
 extern Name attnumAttName(Relation rd, int attid);
 extern Oid	attnumTypeId(Relation rd, int attid);
 extern Oid	attnumCollationId(Relation rd, int attid);
+extern bool isQueryUsingTempRelation(Query *query);
 
 #endif   /* PARSE_RELATION_H */