callback property from 'render panel' to 'render region', changed some
variable names inside the plugins. Not all working yet, though.

submit callbacks.

#683162: Convert all plugins to use new $plugin = array() format. This is less brittle than the specially named hook.

Some major restructuring, catching up to CTools. This is very much in process, there is a huge list of things that need to happen here still, but this may be checkpoint usable to the strong-stomached.

Initial D6 work -- this includes only panels.module stuff. Right now the drag & drop display editor works, layout, layout settings and render works. Special features such as cache and styles may or may not work.