Update V8 to r4588

We're using WebKit r58033, as used by
http://src.chromium.org/svn/releases/5.0.387.0/DEPS
This requires http://v8.googlecode.com/svn/trunk@4465 but this version has a
crashing bug for ARM. Instead we use http://v8.googlecode.com/svn/trunk@4588,
which is used by http://src.chromium.org/svn/releases/6.0.399.0/DEPS

Note that a trivial bug fix was required in arm/codegen-arm.cc. This is guarded
with ANDROID. See http://code.google.com/p/v8/issues/detail?id=703

Change-Id: I459647a8286c4f8c7405f0c5581ecbf051a6f1e8
diff --git a/src/d8.h b/src/d8.h
index c93ea46..30f04c7 100644
--- a/src/d8.h
+++ b/src/d8.h
@@ -117,6 +117,7 @@
                             Handle<Value> name,
                             bool print_result,
                             bool report_exceptions);
+  static const char* ToCString(const v8::String::Utf8Value& value);
   static void ReportException(TryCatch* try_catch);
   static void Initialize();
   static void OnExit();
@@ -175,6 +176,7 @@
   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);