laravel/framework — pull request #2378 by n00ge (2013-10-02 03:50:47+00:00)
Title: Allow for the name of the relation on belongsToMany to be manually defined

As other relationships allow for the name of the relationships to be manually defined, it makes sense for belongsToMany to have that same functionality. If the call to the method is from a magic method using $callers['function'] will not suffice.