Squashed 'framework/yii/' changes from 72100b6..28f8e98


git-subtree-dir: framework/yii
git-subtree-split: 28f8e98757f4faa560e0801a0b8057459ed9cc6e
Merge commit '3b5d218c8ccf7a523bdac3b8d7cd36deda90bfab' into develop. Update yii framework to version 1.1.15.