#311192: Significant refactoring of the menu system; arguments at various non-override paths should now be operational, along with some other intelligent additions to the system.

Fixed (boneheaded) bug that was preventing more than one overriding panel page from storing the backup router data properly.

This fix will _hopefully_ also take care of lots of unhelpful watchdog 'Specialized Panels router rebuild failed...' errors.

Miscellaneous notice cleanups, flexible.incfixes, an aborted attempt at doing preview that needs more thought.

Got rid of a leftover use of $panel_page->pid, and updated the alternate admin menu structure to the current approach.

Some refactoring, partially to accommodate changes suggested by douggreen. The basic context-loading problem has not yet been solved, however.

Created a second admin loader for callbacks that need to generate an edit cache (for ajax callbacks)

Rolled back earlier changes to admin path schema - $panel_page->name now precedes the action verb (e.g. edit, export) again.

Reinstated the %map arg on several admin callbacks; changed the storage mechanism for the loader flags;

Removed suuuuuper crufty ajax functions - they hadn't been in use for who knows how many months, and nobody noticed :)

Fairly large reorganization, although not much change in the logic. Most notable big item is that hook_menu() and hook_menu_alter() are now separate again, and the functions have been reorganized to place the two that hook_menu() calls at the top of the file (purely for conceptual clarity).

Also switched over to the use of a 'flags' field in the router quickref table, which is where we tuck as much of our behavior-governing bitmask as possible during the actual menu build process.

We're most of the way there! Our separate data storage mechanism appears to be mostly working. Now the frontend loading needs to be done, along with the hook_menu_link_alter() stuff.

Panels Page now installs successfully, although the schema is likely going to change. The essential infrastructure for the menu system is functioning correctly. The secondary router storage mechanism, page callbacks, temporary panel data storage mechanism (for render callbacks) and a few other things need to be designed - but we're on the home stretch.

Nearly there. Just need to write the storage mechanism for overridden loaders, then can start debugging.

About three-quarters of the way through the menu system port. Most of the guts are in place, although the bitmasks need considerable work and I've yet to work out a finite solution for sticking the admin tabs in wherever they might need to be.