[development] make a hook_theme_variables that extends the job of _phptemplate_variables

one of the most useful things about PHPTemplate is the template.php file. One of the most useful things about template.php is the _phptemplate_variables. Why don't we extend this to be a module hook that lets module access the variable stack prior to being sent to any template? This would solve the problem that I ran into in page_title.module where the module is dependent on an alteration to the _phptemplate_variables function.