+/* Start the remote shell. cmd may be NULL to use the default. */
+/* TODO: When the shell exits, look at its return value, as this may
+ * well tell us if something went wrong in trying to connect to the
+ * remote machine. Although it doesn't seem to be specified anywhere,
+ * ssh and the shell seem to return these values:
+ *
+ * 124 if the command exited with status 255
+ * 125 if the command is killed by a signal
+ * 126 if the command cannot be run
+ * 127 if the command is not found
+ *
+ * and we could use this to give a better explanation if the remote
+ * command is not found.
+ */