client: Delete socket before opening it again (fixes a panic).

src/bin/client.rs

-use std::fs::create_dir_all;
+use std::fs::{create_dir_all, remove_file};
 use std::sync::Arc;
 use std::ffi::{OsStr, OsString};
 
 
     // We create the socket before starting synchronization, so that the unwrap() below does not
     // cause corruption.
+    remove_file(paths::client_socket()).ok();
     let mut listener = UnixListener::bind(paths::client_socket()).unwrap();
     let mut incoming = listener.incoming();