+/*
+ * Receive a line of input from the current player.
+ * If the player's aborted flag is set, return -2 without receiving
+ * input.
+ * Else receive one line and store it in CMD[SIZE].
+ * This may block for input, yielding the processor. Flush buffered
+ * output when blocking, to make sure player sees the prompt.
+ * If the player's connection has the I/O error indicator set, or the
+ * line is "aborted", set the player's aborted flag and return -2.
+ * If the player's connection has the EOF indicator set, or the line
+ * is "ctld", return -1.
+ * Else return the length of the line.
+ * Design bug: there is no way to indicate truncation of a long line.
+ */