When might a module's weight in the system table not affect its hook order? I am trying to implement hook_menu_alter in my module, but I am finding that revisioning_menu_alter is always being called after my hook, regardless of what I set my module's weight to.  It seems that this is because the revisioning module does not appear in the system table at all, even though it is enabled.

What is going on?  How can I make my module's hook get called after revisioning's hook?  Don't modules always have to have an entry in the system table?
If revisioning does not appear in the system table, it is considered not installed and hook implementations it provides are not executed.

Upon installation, the revisioning module updates its weight to 1, making its hook implementations run later than those of most other modules (which default to a weight of 0).

If you want to change the order in which implementations of a particular hook are executed, have a look at hook_module_implements_alter().