Missing join-tables added in example

There are 2 many-to-may associations between the users and comments. Both use another join-table. The join-tables user_favorite_comments and user_read_comments must be specified. Otherwise the default "user_comment" is taken twice, resulting in an error. 

See https://groups.google.com/forum/#!topic/doctrine-user/Kti36_n6490 and https://groups.google.com/forum/#!topic/doctrine-user/TYwafhgYiSU