refresh libusual

diff --git a/lib b/lib
index 968e99f7539c841dd8fe8ff3420610ad1574b5e9..4d87d575df228ffc1e4c29c112b260ab9baf61b7 160000 (submodule)
--- a/lib
+++ b/lib
@@ -1 +1 @@
-Subproject commit 968e99f7539c841dd8fe8ff3420610ad1574b5e9
+Subproject commit 4d87d575df228ffc1e4c29c112b260ab9baf61b7