Removing plural from httpcache stats' value names.
Add middleware support for real HTTP caching. Add httpcache setting to allow either real or dummy HTTP caching (for backwards compatibility it's set to use dummy cache by default).
Add middleware support for the 'no-store' Cache-Control directive.
Add cache storage support for real HTTP caching. Add real HTTP caching unit tests for both middleware and cache storage.
Updated the downloader middleware documentation to reflect changes introduced by the support for real HTTP caching.
Implemented policies for HTTP Cache
Remove plural from stat key.
Implement single HTTP cache policy
Merge branch 'master' of git://github.com/scrapy/scrapy into http-cache-middleware
Instead of extending from HttpCachePolicy, following the same approach used for storage selection
default httpcache to rfc2616 policy and improve storage and policy tests
requests with no-cache set must force revalidation of cached responses
Merge branch 'http-cache-middleware', remote-tracking branch 'dangra/http-cache-middleware' into http-cache-middleware
Update downloader middleware documentation
More httpcache updates

* Change default cache policy to RFC2616
* Update HttpCacheMiddleware documentation
* Move policies to scrapy.contrib.httpcache
* remove a lint error for .has_key() usage in DBM storage backend
Merge branch 'http-cache-middleware'

Conflicts:
	scrapy/contrib/downloadermiddleware/httpcache.py
	scrapy/contrib/httpcache.py
	scrapy/tests/test_downloadermiddleware_httpcache.py
django is an optional_features, its imports must not fail