Add boolean at remove_meta_box action

[Rahe]

Add the possibility of getting the status of the remove_meta_box action by boolean.
Can be useful if you want to add/remove other metaboxes if one other is present or not.

[nacin]

Needs docs too.

Also, once it's found it, it can just return true immediately. Then return false at the end. No need for the flag.

[markjaquith]

refresh

[markjaquith]

The patch as written won't work. It's doing an isset check, so will continue returning true every time it is called. Furthermore, the function needs to set the value to false even if it isn't already set, because for core meta boxes this acts as a forward-block on the meta box (i.e. calling add later won't work, because it has been marked as pre-removed).

I also don't see the value of this return value. After calling it, it should be removed. Why do you care whether it was already marked as removed or not?