Add os.unsetenv to d8.

src/d8.h

 // Copyright 2009 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 157 matching lines @@
   // os.umask(alue) calls the umask system call and returns the old umask.
   //
   // os.mkdirp(name, mask) creates a directory.  The mask (if present) is anded
   // with the current umask.  Intermediate directories are created if necessary.
   // An exception is not thrown if the directory already exists.  Analogous to
   // the "mkdir -p" command.
   static Handle<Value> OSObject(const Arguments& args);
   static Handle<Value> System(const Arguments& args);
   static Handle<Value> ChangeDirectory(const Arguments& args);
   static Handle<Value> SetEnvironment(const Arguments& args);
+  static Handle<Value> UnsetEnvironment(const Arguments& args);
   static Handle<Value> SetUMask(const Arguments& args);
   static Handle<Value> MakeDirectory(const Arguments& args);
   static Handle<Value> RemoveDirectory(const Arguments& args);
 
   static void AddOSMethods(Handle<ObjectTemplate> os_template);
 
   static Handle<Context> utility_context() { return utility_context_; }
 
   static const char* kHistoryFileName;
   static const char* kPrompt;
@@ skipping 28 matching lines @@
   const char* name_;
   LineEditor* next_;
   static LineEditor* first_;
 };
 
 
 }  // namespace v8
 
 
 #endif  // V8_D8_H_