libbe(3): Document that we'll clobber previous errors set by set_error

lib/libbe/be_error.c

@@ -107,7 +107,6 @@ int
 set_error(libbe_handle_t *lbh, be_error_t err)
 {
 
-	/* XXX TODO: should the old error be overwritten or no? */
 	lbh->error = err;
 	if (lbh->print_on_err && (err != BE_ERR_SUCCESS))
 		fprintf(stderr, "%s\n", libbe_error_description(lbh));

lib/libbe/be_impl.h

@@ -64,6 +64,7 @@ typedef struct prop_data {
 int prop_list_builder_cb(zfs_handle_t *, void *);
 int be_proplist_update(prop_data_t *);
 
+/* Clobbers any previous errors */
 int set_error(libbe_handle_t *, be_error_t);
 
 #endif  /* _LIBBE_IMPL_H */