Hi Chanaka,
I stumbled upon this piece of code (random pick) :
PMA_CommonFunctions::getInstance()->backquote($_REQUEST['view']['name'])
and it made me wonder if using a singleton for PMA_CommonFunctions is necessary, because basicaly PMA_Commonfunctions is a collection of methods, not really a 'living' object. So then I had a look at the class, and I discovered that the class has no class variables (apart from the _instance variable) and an empty constructor. So basicly this should be a static class, with static methods, because no instance is needed for it to work.
And the above piece of code will become :
PMA_CommonFunctions::backquote($_REQUEST['view']['name'])
BTW: If you convert it to a static class, don't forget to replace the $this->method() calls by the static equivalent self::method(). BTW2 : you forgot to add the if (! defined('PHPMYADMIN')), check in the beginning of the file, see [0].
[0] http://wiki.phpmyadmin.net/pma/File_template