1) Exposes Local<Context> v8::Debug::GetDebugContext().
Rationale: We can already get debugger context instance using various workarounds,
so exposing it explicitly in the API only makes things more clear.

2) Removes debugger.HasJavaScriptFrames() requirement for entering debugger context.
Rationale: Sometimes we'd like to call into debugger from the external native code.

3) Makes Debugger v8::Debug::Call execute on debugger context's global object.
Rationale: This is somewhat arguable, but temporary measure. We've agreed that we
should introduce a DebugAPI object that would expose necessary API in the debug-delay.
The problem is that it would take some time to define this API and it is not really
convenient to do that on the v8 land given the difference in v8 / host lifecycle.
The plan is to compose this API as a Debug.* wrapper outside v8 by means of exposing
debugger context's global object here, and once API settles down, upstream it to v8 and
start making Debug::Calls on this new DebugAPI object instead.


git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4251 ce2b1a6d-e550-0410-aec6-3dcde31c8c00