Merge pull request #26 from Wavo/master

Updated version of stack-trace module
Make development and test default dev environments

It's uncommon to want exceptions to go to Airbrake's servers in development mode and during test runs.
Merge pull request #28 from stephencelis/patch-1

Make development and test default dev environments
Add accept header for compatiblity with errbit.

Otherwise Errbit responds with 406 Not Acceptable.
Merge pull request #29 from dylanahsmith/accept_xml

Add accept header for compatiblity with errbit.