manager.py should not use hardcoded 'id'

[marcofalcioni]

line 42 and 172 should use 'pk' instead of 'id' I think. I am trying to verify this. I'll post updates when I do.

[M1ha-Shvn]

Hi, thanks for reporting.
I suppose, you are right, but it's a little bit more complex. ReturningQuerySet gets data with native database column names. Its values_list method is not django one, it doesn't know, what field is a primary key. So what can be done is:

1. Fetching pk name from django model in manager.py and getting it instead of id
2. Resolving column names like pk inside ReturningQuerySet based on it's model and replacing id to pk in manager.py.

To my mind second way is more pretty.

I'm sorry, but I have no time for fixing it this week. I'll have a look in 2-3 weeks. If you want it faster - please, make a PR and I'll accept it.

[M1ha-Shvn]

Released 1.2.2