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

src/tool_getparam.c

@@ -180,6 +180,7 @@ static const struct LongShort aliases[]= {
   {"$P", "service-name",             TRUE},
   {"$Q", "proto-default",            TRUE},
   {"$R", "expect100-timeout",        TRUE},
+  {"$S", "tftp-no-options",          FALSE},
   {"0",   "http1.0",                 FALSE},
   {"01",  "http1.1",                 FALSE},
   {"02",  "http2",                   FALSE},
@@ -1005,6 +1006,9 @@ ParameterError getparameter(char *flag,    /* f or -long-flag */
         if(err)
           return err;
         break;
+      case 'S': /* --tftp-no-options */
+        config->tftp_no_options = toggle;
+        break;
       }
       break;
     case '#': /* --progress-bar */