Fixed #9204 -- Added `GIcon` overlay, allowing customization for icons of...

Fixed #9204 -- Added `GIcon` overlay, allowing customization for icons of `GMarker` objects.  Thanks to qingfeng for initial ticket/patch, and to prairiedogg for final implementation.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@10021 bcc190cf-cafb-0310-a4f2-bffc1f526a37