[1.2.X] Fixed #14133 -- Updated Windows installation instructions for...

[1.2.X] Fixed #14133 -- Updated Windows installation instructions for GeoDjango, now recommend the OSGeo4W installer for spatial libraries.

Backport of r15872 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@15873 bcc190cf-cafb-0310-a4f2-bffc1f526a37