TFTP: add option to suppress TFTP option requests (Part 2)

- Add tests.

- Add an example to CURLOPT_TFTP_NO_OPTIONS.3.

- Add --tftp-no-options to expose CURLOPT_TFTP_NO_OPTIONS.

Bug: https://github.com/curl/curl/issues/481

lib/tftp.c

@@ -978,7 +978,7 @@ static CURLcode tftp_connect(struct connectdata *conn, bool *done)
       return CURLE_OUT_OF_MEMORY;
   }
 
-  /* we don't keep TFTP connections up bascially because there's none or very
+  /* we don't keep TFTP connections up basically because there's none or very
    * little gain for UDP */
   connclose(conn, "TFTP");