Use RtlCaptureContext instead of inline assembly to capture execution context on...

Use RtlCaptureContext instead of inline assembly to capture execution context on Windows

Inline assembly is not available in Visual C++ 64-bit version so use RtlCaptureContext to capture execution context. RtlCaptureContext is not available on Windows 2000 so this change removes Windows 2000 support. If this turns up causing trouble we can revert to only use RtlCaptureContext in 64-bit and inline assembly in 32-bit.
Review URL: http://codereview.chromium.org/335008

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@3122 ce2b1a6d-e550-0410-aec6-3dcde31c8c00