Use menu_get_item instead of debug_backtrace to determine context

While I certainly see the point of #1, I still cannot abide running debug_backtrace() in production code. At the same time, it would not do to introduce such a large regression, particularly when there are significant numbers of people who do not share that feeling.

Perhaps this patch might be a suitable compromise.

* menu_get_item() is still used in the primary handler to find the node or taxonomy term of the current menu item, as applicable, as it is not the introduction of menu_get_item(), but the removal of debug_backtrace() that introduces the regression in behavior. (Note also that this version of the patch fixes a serious problem in #0 -- $data['user'] should not be assigned the user from menu_get_item(), because that would return the user being viewed on the current user page, and it would not do to have the token [user:name] sometimes refer to the logged-in user, and sometimes review to the user on the page being viewed.)

* A call to drupal_alter() is introduced, so modules such as Page Manger and Panels can add information to $data and $options based on context in some future release (if desired).

* For backwards compatibility with the existing release of token_filter, the special code that uses debug_backtrace() is moved to a submodule, token_filter_advanced(), that implements the appropriate hook to fill in $data and $options, exactly as it did before.

* A hook_update_N() is also provided to enable token_filter_advanced for all current users of token_filter, so that the capabilities of the module do not suddenly change due to a minor update. New users of the module must explicitly enable token_filter_advanced.

The latest suggested patch (#2) should behave the same as the current code; it just gives folks the option to turn of the hook that contains debug_backtrace by disabling the new module added in the patch. Those who chose to disable the new module would have problems per #8, but by default, the new module is enabled by the update hook, so existing users should be unaffected.