Retry errors which indicate the connection closed prematurely.

See discussion in #442

fs/closed_conn.go

@@ -0,0 +1,9 @@
+// +build !windows
+
+package fs
+
+// isClosedConnErrorPlatform reports whether err is an error from use
+// of a closed network connection using platform specific error codes.
+func isClosedConnErrorPlatform(err error) bool {
+	return false
+}