Small misspelling

I think, the correct form is `should be defined` OR `is defined`, but not `be defined`

Path was wrong

Fixes #3048: emphasized that sourcePath in asset bundle means "copy all the contents of it to the web/assets"

http://www.yiiframework.com/forum/index.php/topic/53430-appasset-questions-getting-404-error-on-asset-files/page__gopid__246055#entry246055

Add `whenClient` description

fixes for https://github.com/yiisoft/yii2/issues/951#issuecomment-25934549

added predefined path aliases of advanced yii application template

just a type correction and suggestion on adding a comma and one word (ie 'by') to make it more easily to be understand.

Re-implemented RBAC by following more closely to the original NIST RBAC model. Dropped `yii\rbac\PhpManager`.

fixes #1581 and #3013

added a hint and link