Improved documentation for php expressions

Fixes issue #1921
Various documentation and code style fixes
Merge branch 'master' of https://github.com/yiisoft/yii

* 'master' of https://github.com/yiisoft/yii:
  fixing bug where time() was being added twice to the cookie expiration date. Once before we pass it to CWebUser::saveToCookie, and another time inside the function.
  oops, did not notice that changelog entries are ordered by type then number
  Fixing CWebUser#restoreFromCookie to respect identityCookie options as well. Adding changelog line
  Fixing bug in CWebUser#renewCookie which was causing it to ignore any configuration parameters speicified in user => identityCookie