Add os.chdir and os.setenv to d8. Move system() to os.system().

src/d8.h

Index: src/d8.h
===================================================================
--- src/d8.h	(revision 1633)
+++ src/d8.h	(working copy)
@@ -130,9 +130,12 @@
   static Handle<Value> Quit(const Arguments& args);
   static Handle<Value> Version(const Arguments& args);
   static Handle<Value> Load(const Arguments& args);
-  // system("program_name", ["arg1", "arg2", ...], timeout1, timeout2) will run
-  // the command, passing the arguments to the program.  The standard output of
-  // the program will be picked up and returned as a multiline string.  If
+  // The OS object on the global object contains methods for performing
+  // operating system calls:
+  //
+  // os.system("program_name", ["arg1", "arg2", ...], timeout1, timeout2) will
+  // run the command, passing the arguments to the program.  The standard output
+  // of the program will be picked up and returned as a multiline string.  If
   // timeout1 is present then it should be a number.  -1 indicates no timeout
   // and a positive number is used as a timeout in milliseconds that limits the
   // time spent waiting between receiving output characters from the program.
@@ -140,7 +143,16 @@
   // milliseconds on the total running time of the program.  Exceptions are
   // thrown on timeouts or other errors or if the exit status of the program
   // indicates an error.
+  //
+  // os.chdir(dir) changes directory to the given directory.  Throws an
+  // exception/ on error.
+  //
+  // os.setenv(variable, value) sets an environment variable.  Repeated calls to
+  // this method leak memory due to the API of setenv in the standard C library.
+  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<Context> utility_context() { return utility_context_; }