FIX: belongs_many_many back to the same class type

Currently SS get's confused when referencing multiple of the same DataObject type in a belongs_many_many definition using the dot notation.  It doesn't recognize the dot notation at all, and leaving it off means it will just choose the first match in the many_many definition which isn't correct.  This adds in the dot check and reverse lookup functionality allowing for multiple definitions.

I couldn't find a bug referencing it specifically however there's lots of discussion in the forums and IRC so this problem does in fact exist.
Why was this removed?