Provide an hook for context_handler_pre_render

Currently there's no way (that I know of) to interact with the contents of a panel/page, and act upon it's values before it's rendered. I stumbled upon this problem with the current way I've developed Panels Breadcrumbs, that sets the breadcrumbs at hook_ctools_render_alter(). While it works quite nicely if you simply print $breadcrumbs at theme time, if you show the breadcrumbs through panels as pane, the pane that holds the breadcrumb will have been rendered before ctools_render_alter gets called, meaning, no custom breadcrumbs pane.

Looking through the code I found that "all" handlers call ctools_context_handler_pre_render, but as of version 7.x-1.0-rc1 it hasn't been implemented.