Use option name --test-commandline in tor-fw-helper.

It was previously --Test in the help output and --test-commandline in
the getopt call. The man page already had --test.

  (Originally by David, who resolved the tie in favor of "--test"; I
   chose --test-commandline" instead so that nothing that depended
   on it could break. -Nick)

changes/bug7768

   o Documentation fixes:
-    - Update tor-fw-helper.1.txt to describe its options with their
-      correct names. Fixes bug 7768.
+    - Update tor-fw-helper.1.txt and tor-fw-helper.c to make option
+      names match. Fixes bug 7768.

src/tools/tor-fw-helper/tor-fw-helper.c

@@ -97,7 +97,7 @@ usage(void)
 {
   fprintf(stderr, "tor-fw-helper usage:\n"
           " [-h|--help]\n"
-          " [-T|--Test]\n"
+          " [-T|--test-commandline]\n"
           " [-v|--verbose]\n"
           " [-g|--fetch-public-ip]\n"
           " [-p|--forward-port ([<external port>]:<internal port>])\n");