Defer storing the session until it has a value set
Properly close the WriteFlusher instance

Based on @klauspost's suggestion
Merge pull request #597 from revel/close-compress-writer

Properly close the WriteFlusher instance
Merge pull request #587 from revel/pushrax/defer-sessions

Defer storing the session until it has a value set
Redis Cache: Save a roundtrip on delete

Don't have a separate "exists" roundtrip when deleting a key, simply
read from the return value from the delete operation itself.
Merge pull request #603 from klauspost/develop

Redis Cache: Save a roundtrip on delete
Allow errors from redis delete calls to be returned

Extension to #603