Make sure Reason is a string

Since 8194983c4686945850b142e3cf330c8795a859b6 when an exception
in the app occured the console had:

Bad value on output port 'efile'

and the error log remained empty. This was due to the tupe not being
converted to string.
Merge pull request #176 from agx/fixes/error_logger

Make sure Reason is a string