Since Python 2.6, the BaseException.message attribute is deprecated (PEP-352[1])
in favor of e.args[0] or str(e). This commit replaces e.message with str(e).
[1] https://www.python.org/dev/peps/pep-0352/
Signed-off-by: Maël Kerbiriou <m431.kerbiriou@gmail.com>