test_whisper.py: use unittest2 if it is available
test_whisper.py: use unittest2 if it is available

graphite-project/whisper,akbooer/whisper,obfuscurity/whisper,piotr1212/whisper,cbowman0/whisper,penpen/whisper,graphite-server/whisper,deniszh/whisper,jjneely/whisper,alexandreboisvert/whisper,acdha/whisper,kerlandsson/whisper