#307628: Fixed creation of $panel_args in the panel_page menu handling system to contain raw id values, as expected by views and node content for string substitution.

Updated general panels_page settings form validation to prevent errors resulting from names consisting only of numbers. (Fwd port from d5)

#314495: Tab to change layout of panel node missing; also fix menu items so they only show up for panel nodes.

Updated context callback to comply with changes stemming from the D6 menu system. (Can handle both a uid and a fully-loaded user object, now)

Updated panels_panels_include_directory() docblock to correct errors and provide a better explanation.

#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.

Unified context id generation into a single callback, panels_context_id(). The output pattern is identical to before, just a little less code overhead.