sql.py: put_table(): Fixed bug where mapping was still a plain dict because that's what dicts.join() returns, by moving the wrapping of it in a sql_gen.ColDict after dicts.join()

sql_gen.py: ColDict: Fixed bug where copy() needed to be implemented

sql.py: into_table_name(): Fixed bug where key needed to be passed through str() now that ColDict uses Col objects for everything

sql_gen.py: ColDict: Extend UserDict.DictMixin instead of dict because its non-core function implementations route all inner dict accesses to the core functions getitem() and setitem(). sql.py: put(): DuplicateKeyException: Wrap util.dict_subset_right_join() in a sql_gen.ColDict because the dict returned by util.dict_subset_right_join() is just a plain dict. (This change must happen at the same time because the previous functionality relied on a bug in ColDict.)

util.py: DefaultDict: Use dicts.DictProxy instead of collections.defaultdict so that it provides a view of the given dict instead of copying it

dicts.py: Added DictProxy

sql.py: mk_select(): conds: Support dict-like objects other than dict itself (such as sql_gen.ColDict)

dicts.py: Added is_dict()

sql.py: DbConn.DbCursor.execute(): When setting self.query, provide default values for query, params because some debug printing statements use self.query directly instead of _add_cursor_info()

sql.py: insert(): Fixed bug where column remaing needed to be removed and sql_gen.Literal value unwrapped