dont add table to query(from_obj) if the table is already present in the from_obj list

[Former user]

(original reporter: anonymous) this will allow people to more easily make custom join conditions when querying.

[Former user]

(original author: anonymous) fyi we are talking about lines 346 and 379 of sqlalchemy/orm/query.py...a conditional needs to be added along the lines of :

        alltables = sum([for x in from_obj](sql_util.TableFinder(x)))
        if self.table not in alltables:
               from_obj.append(self.table)

[Mike Bayer]

implemented this with some unit tests in changeset:1904