build_solr_schema tries to use None as a HAYSTACK_CONNECTIONS key

Hiya,

While trying to run the management command ``python manage.py build_solr_schema`` it wasn't picking up the default ``HAYSTACK_CONNECTIONS`` option, It was getting a ``None`` as the engine key.

 {'settings': None, 'pythonpath': None, 'verbosity': '1', 'traceback': None, 'filename': None, 'using': None}

I've added ``default`` parameter  to ``make_option``

{'settings': None, 'pythonpath': None, 'verbosity': '1', 'traceback': None, 'filename': None, 'using': 'default'}

This was using Django 1.3 and Python 2.7. Hopefully I am making some sense, please let me know if not!

Cheers!


A