Add test_as_dict_no_column_name, test_as_dict_no_column_name_2

Add tests for when as_dict=True and columns missing names.
execute: Raise ColumnsWithoutNamesError when as_dict=True and missing
column names
Merge pull request #160 from pymssql/as_dict_No_column_name_raise_exception2

Raise exception if as_dict=True and column(s) have no names