Fix typos in exttablecmds.c comments

src/backend/commands/exttablecmds.c

@@ -48,10 +48,10 @@ static void InvokeProtocolValidation(Oid procOid, char *procName, bool iswritabl
 * In here we first dispatch a normal DefineRelation() (with relstorage
 * external) in order to create the external relation entries in pg_class
 * pg_type etc. Then once this is done we dispatch ourselves (DefineExternalRelation)
-* in order to create the pg_exttable entry accross the gp array.
+* in order to create the pg_exttable entry across the gp array.
 *
-* Why don't we just do all of this in one dispatch run? because that
-* involves duplicating the DefineRelation() code or severly modifying it
+* Why don't we just do all of this in one dispatch run? Because that
+* involves duplicating the DefineRelation() code or severely modifying it
 * to have special cases for external tables. IMHO it's better and cleaner
 * to leave it intact and do another dispatch.
 * ----------------------------------------------------------------