Make error message of pageinspect more consistent for raw page inputs

There is a copy-paste error from bt_page_items() which got into
bt_page_items_bytea().  A second message in get_raw_page_internal() was
inconsistent with all the other sub-modules.

Author: Ashutosh Sharma
Discussion: https://postgr.es/m/CAE9k0PnZuZ3PVXSyQY91-53E8JKFcaSyknFqqU43r9MabKSYZA@mail.gmail.com

contrib/pageinspect/btreefuncs.c

@@ -429,7 +429,7 @@ bt_page_items_bytea(PG_FUNCTION_ARGS)
 	if (!superuser())
 		ereport(ERROR,
 				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
-				 (errmsg("must be superuser to use pageinspect functions"))));
+				 (errmsg("must be superuser to use raw page functions"))));
 
 	if (SRF_IS_FIRSTCALL())
 	{

contrib/pageinspect/rawpage.c

@@ -102,7 +102,7 @@ get_raw_page_internal(text *relname, ForkNumber forknum, BlockNumber blkno)
 	if (!superuser())
 		ereport(ERROR,
 				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
-				 (errmsg("must be superuser to use raw functions"))));
+				 (errmsg("must be superuser to use raw page functions"))));
 
 	relrv = makeRangeVarFromNameList(textToQualifiedNameList(relname));
 	rel = relation_openrv(relrv, AccessShareLock);