don't rely on pk-only group_by
don't rely on pk-only group_by

Fixed the test test_aliased_stmt_includes_unnamed_fn
recently added in c1c999c01d to include the additional
column in the GROUP BY statement, allowing this statement
to succeed on SQL Server which seems to not support "group by pk only"
syntax.

Change-Id: I42184d77c9017ebdb76ac5a9ae1f8128561243ec

sqlalchemy/sqlalchemy,zzzeek/sqlalchemy,j5int/sqlalchemy,j5int/sqlalchemy,monetate/sqlalchemy,monetate/sqlalchemy