Added getter for cell contents to CGridColumn

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

issue #106
Merge branch 'master' into 106-cgridcolumn-extend

* master: (741 commits)
  fixed test break for php < 5.3.0
  better fix for #2378
  CHANGELOG line for #2777
  guide fix about autoloading
  Re-added call to Yii::autoload to import() to keep speed
  Replaced explicit call to Yii::autoload() with call to autoloader stack
  fixed CApplication docs about autoloader
  fixed formatting, adjusted changelog
  Changing from "ob_end_flush" to "ob_end_clean"
  Changelog update
  Code formatting
  Handle thrown exception in widgets when 'captureOutput' is set to true.
  [UK][Guide] typos  [ci skip]
  Issue #2654 has been added to CHANGELOG
  CDbCommand::buildQuery() no longer throw exception if 'from' is missing.
  Unnecessary comment at CErrorHandler::render() has been removed.
  Chapter 'Using 3rd-Party Autoloaders' has been added to guide
  CErrorHandler::errorAction via AJAX has been added to UPGRADE
  Issue #2753 has been added to CHANGELOG
  CErrorHandler has been refactored to respect errorAction on AJAX request.
  ...

Conflicts:
	CHANGELOG
better fix for #106 according to discussion in #2052
adjusted the default Grid column classes to changes made in #2052

use get...Content() instead of render...Content()
Merge pull request #2052 from cebe/106-cgridcolumn-extend

Added getter for cell contents to CGridColumn