Summary of the changes:
* Add thread_safe gem.
* Use thread safe cache for digestor caching.
* Replace manual synchronization with ThreadSafe::Cache in Relation::Delegation.
* Replace @attribute_method_matchers_cache Hash with ThreadSafe::Cache.
* Use TS::Cache to avoid the synchronisation overhead on listener retrieval.
* Replace synchronisation with TS::Cache usage.
* Use a preallocated array for performance/memory reasons.
* Update the controllers cache to the new AS::Dependencies::ClassCache API.
The original @controllers cache no longer makes much sense after @tenderlove's
changes in 7b6bfe84f3 and f345e2380c.
* Use TS::Cache in the connection pool to avoid locking overhead.
* Use TS::Cache in ConnectionHandler.
This will be used to derive keys from the secret and a salt, in order to allow us to
do things like encrypted cookie stores without using the secret for multiple
purposes directly.
