Fixed json stringifying with circular object references.

Errors caught via domains exhibit this issue.

http://stackoverflow.com/questions/11616630/json-stringify-avoid-typeerror-converting-circular-structure-to-json
Revert "Fixed json stringifying with circular object references."

This reverts commit 8b4cff1e9b09f24ae5919a0b2f1845ea4b62521c.
Prevented circular object references using json-stringify-safe
add test for circular object references