Fix debugger interaction due new DAL

Originally, __all__ was used to filter DAL and Field globals, but now the new module doesn't explicity set that attribute, so this filter was removed.
Note that using __dict__ as a replacement is not an option, as the new dal module exports a lot of common names like connection, base, etc.
For more info, see:
https://groups.google.com/d/msg/web2py/zbSgN5qAQi0/pBWjsv6EElAJ