Put back allow_system_table_mods check in heap_create().

This reverts commit a475c60367.

Erik Rijkers reported back in January 2013 that after the patch, if you do
"pg_dump -t myschema.mytable" to dump a single table, and restore that in
a database where myschema does not exist, the table is silently created in
pg_catalog instead. That is because pg_dump uses
"SET search_path=myschema, pg_catalog" to set schema the table is created
in. While allow_system_table_mods is not a very elegant solution to this,
we can't leave it as it is, so for now, revert it back to the way it was
previously.

src/backend/bootstrap/bootparse.y

@@ -222,7 +222,8 @@ Boot_CreateStmt:
 												   RELKIND_RELATION,
 												   RELPERSISTENCE_PERMANENT,
 												   shared_relation,
-												   mapped_relation);
+												   mapped_relation,
+												   true);
 						elog(DEBUG4, "bootstrap relation created");
 					}
 					else

src/backend/catalog/heap.c

@@ -246,7 +246,8 @@ heap_create(const char *relname,
 			char relkind,
 			char relpersistence,
 			bool shared_relation,
-			bool mapped_relation)
+			bool mapped_relation,
+			bool allow_system_table_mods)
 {
 	bool		create_storage;
 	Relation	rel;
@@ -254,6 +255,18 @@ heap_create(const char *relname,
 	/* The caller must have provided an OID for the relation. */
 	Assert(OidIsValid(relid));
 
+	/*
+	 * sanity checks
+	 */
+	if (!allow_system_table_mods &&
+		(IsSystemNamespace(relnamespace) || IsToastNamespace(relnamespace)) &&
+		IsNormalProcessingMode())
+		ereport(ERROR,
+				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
+				 errmsg("permission denied to create \"%s.%s\"",
+						get_namespace_name(relnamespace), relname),
+		errdetail("System catalog modifications are currently disallowed.")));
+
 	/*
 	 * Decide if we need storage or not, and handle a couple other special
 	 * cases for particular relkinds.
@@ -1132,7 +1145,8 @@ heap_create_with_catalog(const char *relname,
 							   relkind,
 							   relpersistence,
 							   shared_relation,
-							   mapped_relation);
+							   mapped_relation,
+							   allow_system_table_mods);
 
 	Assert(relid == RelationGetRelid(new_rel_desc));
 

src/backend/catalog/index.c

@@ -825,7 +825,8 @@ index_create(Relation heapRelation,
 								RELKIND_INDEX,
 								relpersistence,
 								shared_relation,
-								mapped_relation);
+								mapped_relation,
+								allow_system_table_mods);
 
 	Assert(indexRelationId == RelationGetRelid(indexRelation));
 

src/include/catalog/heap.h

@@ -46,7 +46,8 @@ extern Relation heap_create(const char *relname,
 			char relkind,
 			char relpersistence,
 			bool shared_relation,
-			bool mapped_relation);
+			bool mapped_relation,
+			bool allow_system_table_mods);
 
 extern Oid heap_create_with_catalog(const char *relname,
 						 Oid relnamespace,