Expose more info about post-mortem constants

Useful for node.js and/or other tools.

BUG=
R=danno@chromium.org

Review URL: https://codereview.chromium.org/404173002

Patch from Fedor Indutny <fedor.indutny@gmail.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22549 ce2b1a6d-e550-0410-aec6-3dcde31c8c00