Teach inspectdb to handle SQL column names that are digits.

There's no accounting for taste in the way some people name columns,
apparently. Create a column with a name of "1" and inspectdb will still
produce valid Python code now. Fixed #16536. Thanks tereaom and
danodonovan.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@16641 bcc190cf-cafb-0310-a4f2-bffc1f526a37