As a primary_key field has to be unique, added a check at DataHandler
instanciation to make sure a field set as a pk is not set as non-unique

We delete all results with the same UID...

get_referenced method were implemented for SingleReference and MultipleReference class
They are able to return LeObject instances refereced by them

Hook names were wrong

Deleted old methods that are unused (one of them was triggerring an error will doing nothing)

**kwargs was not given to super() constructor

- a "normal" import was left in lefactory_common
- the hook triggering datasources init in dyncode was not called
- dyncode was not exposed in the loader (making hook call useless : the hook has to be called once the dyncode has been "seen" (imported) by python)

Test passes

When not found return None and do not try to run len() on None

Return an instance and not a list of len 1 anymore

In construct and check data

with make deb . Next commit will update the README

Now backref seems to work at creation of a Person linked with a text the Person UID is appended to Text.linked_persons

Triggered a bug in wrong Integer DH tests

Return the value of this datahandler when empty

refs #131

The dedup mechanism was using a cast of list to set. But sometimes, filters contains list, and list are not hashable...

refs #131