refactored redis cache.
removed unneeded setting.
Merge branch 'master' of github.com:yiisoft/yii2

* 'master' of github.com:yiisoft/yii2:
  removed unneeded setting.
  refactored redis cache.
allow redis connection to be configure directly in cache

fixes #1316
added redis Session

as suggested in issue #1316
fixed cubrid limit
updated properties of extensions
fixed broken sphinx AR::attributes() declaration

Model::attributes() has been made static
Merge branch 'master' into elasticsearch

* master:
  fixed broken sphinx AR::attributes() declaration
  updated properties of extensions
  fixed cubrid limit
  added redis Session
  allow redis connection to be configure directly in cache
  removed unneeded setting.
  refactored redis cache.

Conflicts:
	extensions/redis/README.md