Added the 'references' command to the debugger protocol to provide access to the mirror features of retreiving all the objects referencing a given object and all objects instantiated by a given function.

Added commands 'references' and 'instances' to the developer shell for using this new debugger protocol command.
Review URL: http://codereview.chromium.org/21080

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@1234 ce2b1a6d-e550-0410-aec6-3dcde31c8c00