Don't overwrite a custom message
Merge pull request #15 from Captricity/master

Don't overwrite a custom message
Merge pull request #20 from lusitania/fileConfig

Signature change as proposed in issue #16
Merge pull request #19 from lusitania/py3py2

Py3 compatibility as proposed in issue #17
Merge branch 'master' of https://github.com/airbrake/airbrake-python