Add an argument to copy commands to set the prefix for the buffer name,

allows buffers for different sessions to be named separately.

tty-keys.c

@@ -976,7 +976,7 @@ tty_keys_clipboard(__unused struct tty *tty, const char *buf, size_t len,
 
 	/* Create a new paste buffer. */
 	log_debug("%s: %.*s", __func__, outlen, out);
-	paste_add(out, outlen);
+	paste_add(NULL, out, outlen);
 
 	return (0);
 }