Debug.log output prints to STDOUT instead of STDERR

This is particularly a problem with the JUnit formatting as it means any Debug.log is included in the head of the JUnit output, making it invalid xml.

Steps to reproduce; write a test case with Debug.log, and invoke elm-test with JUnit reporter redirected to an xml file.

If Debug.log went to STDERR it would not be redirected to the file. Alternatively allow Junit reporter to specify a file and only output the test results to the file.