Fixed backtrace in D8 debugger and added gdb like syntax 'bt n' and 'bt -n' in addition to the already existing 'bt from to'.
Review URL: http://codereview.chromium.org/99342

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@1929 ce2b1a6d-e550-0410-aec6-3dcde31c8c00