Merge 'find_changes' into 'DBIx-Class-current'

Merge 'find_changes' into 'DBIx-Class-current'

- add update_or_create_related to Relationship::Base
- add find_or_new to ResultSet/ResultSetProxy and find_or_new_related
 to Relationship::Base
- add accessors for unique constraint names and coulums to
 ResultSource/ResultSourceProxy
- rework ResultSet::find() to search unique constraints
- CDBICompat: modify retrieve to fix column casing when ColumnCase is
 loaded
- CDBICompat: override find_or_create to fix column casing when
 ColumnCase is loaded