fixes missing import that was cuasing 500s of the following type

User: Indigo
Time: 2013-01-30T14:25:10.511340
User-agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.17 (KHTML, like Gecko) Chrome/24.0.1312.56 Safari/537.17
File path /home/ubuntu/class2go/main/accounts/views.py:302
Line text: date.today() >= request.common_page_data['course'].calendar_start :