Merge branch 'release/0.6.8' into develop
Instantiate FakeClient every times.
Problem: Singleton of Fakeclient keeps error state of previous web call which
will eventually raise again on the subsequent call no matter if it is success
or not.
Merge branch 'develop' of https://github.com/ruxo/django-slumber into develop

Conflicts:
	slumber/connector/ua.py
Instantiate FakeClient every times.

Problem: Singleton of Fakeclient keeps error state of previous web call which will eventually raise again on the subsequent call no matter if it is success or not.
Change the instance cache to be thread safe.
Bumped version number.
Merge branch 'release/0.6.9'