Fix for Django 1.3

[sneilan]

To make this software work on Django 1.3, I had to modify lines 46 & 47 in the cache_incr(self, key) function in ratelimitcache.py:

I changed these two lines:
cache._cache.add(key, '0', time=self.expire_after())
cache._cache.incr(key)

To:
cache.add(key, '0', self.expire_after())
cache.incr(key)

I must say, ratelimitcache is a great idea for throttling certain pages!