Refactored compiler SELECT, GROUP BY and ORDER BY generation.
While there, also refactored select_related() implementation
(get_cached_row() and get_klass_info() are now gone!).
Made get_db_converters() method work on expressions instead of
internal_type. This allows the backend converters to target
specific expressions if need be.
Added query.context, this can be used to set per-query state.
Also changed the signature of database converters. They now accept
context as an argument.
Tim Graham
Anssi Kääriäinen
Niclas Olofsson
Jason Myers
Boryslav Larin
Claude Paroz
Aymeric Augustin
Florian Apolloner