joomla/joomla-platform — pull request #1660 by ssv445 (2012-11-02 11:02:09+00:00)
Title: Use include_once

I have found a bug recently, we were trying to autoload JHtmlGrid.
- We tried to autoload class JHtmlGrid
- Joomla autloader loaded libraries/joomla/html/grid.php (class in that file is JGrid)
- then JHtml tried to autoload the same class
- again the same file was included (as class expected in file was not there, so class_exists check failed)

So I propose here that for autoloading purpose, one file should be loaded once.
Added the same change here.