Added getter for cell contents to CGridColumn

Added getters to CGridColumn to allow getting cell contents
for extended use cases of CGridView.

issue #106
Fixes #2254:

1. Fixes original issue: AJAX and client validation doesn't work with `errorSummary` set to true.
2. Added `CForm::$showErrors` which controls whether error elements of the each attribute should be rendered.
PHPDoc fixes:

1. Additional `CForm` class note.
2. Better description of the `CForm::$showErrors`.
Additional explanation of what `CForm::$showErrors` precisely does.
PHPDoc of `CForm::$showErrors` is now a bit less cryptic.
Enhance CJSON with JsonSerializable support (#2540)
Fixed disrespect of overrides of CActiveRecord::attributeNames()
views/ja updated
docs/guide/ja/database.ar.txt updated
docs/blog/ja/start.testdrive.txt updated
Merge pull request #2577 from softark/ja-update-2013-06-21

Ja update 2013-06-21
Bug #2581 ajaxVar in jquery.yiilistview.js
Bug #2581 ajaxVar in jquery.yiigridview.js
fixes #2558: added explaination about boolean arguments usage to migrate docs
Merge pull request #2582 from seregagl/2581-ajaxvar-in-clistview

Bug #2581 ajaxVar in jquery.yiilistview.js
fixes #2529: CAssetManager caused chmod() operation not allowed error on NTFS
Merge pull request #2320 from resurtm/fixes-2254

Fixes #2254: AJAX and client validation doesn't work with `errorSummary` set to true.
fixes #2401
Test case "CActiveRecordTest::testCustomAttributes()" has been added.
Code style at "CActiveRecord" has been fixed.