Fixed #13711 -- Model check added to ensure that auto-generated field name is within limits of the database.

...ion.
@timgraham 
I have removed this test because as we discussed and also on the ticket that silent auto-truncation of auto-generated pks in M2M or FK field may cause errors if the initial max_length characters are same.
The test added for the fix of this ticket covers all aspect of dealing with cases here.