Use keyword arguments for redis cache.

StrictRedis has a different argument order for some reason.

Fix #406

Backport of #406, see #610

Conflicts:
	CHANGES
	tests/contrib/test_cache.py
	werkzeug/contrib/cache.py
Merge branch '0.9-maintenance'

Conflicts:
	werkzeug/contrib/cache.py
Don't expire items if they haven't been added