allow specification of which cache is used to store in-progress jobs
future proofs the CRON_CACHE setting value with Django 1.7's changes to the caching API
bumps minor version to 0.3.4
Merge branch 'master' of https://github.com/craiglabenz/django-cron into craiglabenz-master

Conflicts:
	django_cron/management/commands/runcrons.py
	setup.py