9845cd6 broke configuring a cache store like so:
config.cache_store = :redis_cache_store, config_for("redis/cache")
Rails::Application#config_for returns an ActiveSupport::OrderedOptions. By default, the Array#extract_options! core extension won't extract instances of Hash subclasses. Add ActiveSupport::OrderedOptions#extractable_options? and have it return true to fix.
Split up the caching tests as prep for adding a new cache store. Slices
the mega test/caching_test.rb into behavior modules, concrete store
tests, and cross-cutting store tests.
Considering moving cache store behavior modules into lib/ so they may be
used for acceptance testing by third parties.
