Allow for primary log rotation by copy and truncate rather than rename
Merge pull request #2275 branch 'copytruncate' of https://github.com/bdstevens/yii into bdstevens-copytruncate

* 'copytruncate' of https://github.com/bdstevens/yii:
  Allow for primary log rotation by copy and truncate rather than rename
a bit of refactoring for PR #2275 + CHANGELOG line