assert: allow circular references

assert.deepEqual() and assert.deepStrictEqual() will no longer throw a
RangeError if passed objects with circular references.

PR-URL: https://github.com/nodejs/node/pull/6432
Fixes: https://github.com/nodejs/node/issues/6416


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>