Adds a --help option and usage message listing all flags to V8.

samples/shell.cc

 // Copyright 2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 54 matching lines @@
   bool run_shell = (argc == 1);
   for (int i = 1; i < argc; i++) {
     const char* str = argv[i];
     if (strcmp(str, "--shell") == 0) {
       run_shell = true;
     } else if (strcmp(str, "-f") == 0) {
       // Ignore any -f flags for compatibility with the other stand-
       // alone JavaScript engines.
       continue;
     } else if (strncmp(str, "--", 2) == 0) {
-      printf("Warning: unknown flag %s.\n", str);
+      printf("Warning: unknown flag %s.\nTry --help for options\n", str);
     } else if (strcmp(str, "-e") == 0 && i + 1 < argc) {
       // Execute argument given to -e option directly
       v8::HandleScope handle_scope;
       v8::Handle<v8::String> file_name = v8::String::New("unnamed");
       v8::Handle<v8::String> source = v8::String::New(argv[i + 1]);
       if (!ExecuteString(source, file_name, false, true))
         return 1;
       i++;
     } else {
       // Use all other arguments as names of files to load and run.
@@ skipping 163 matching lines @@
     for (int i = 0; i < start; i++) {
       printf(" ");
     }
     int end = message->GetEndColumn();
     for (int i = start; i < end; i++) {
       printf("^");
     }
     printf("\n");
   }
 }