Gracefully handle any errors that occur when attempting to remove the rollback handler.
Gracefully handle any errors that occur when attempting to remove the rollback
handler.

Fixes Issue #64.


jackxiang/google-app-engine-django,ekkleesia3/google-app-engine-django,dila93/google-app-engine-django,termie/google-app-engine-django,hitrust/google-app-engine-django,brian-zhao/google-app-engine-django,google-code-export/google-app-engine-django