CYB-164 https://jira.ets.berkeley.edu/jira/browse/CYB-164  -- previous version was caching with class variables, which are not thread safe, and so are not suitable for use with Apache.
Merge pull request #90 from coyote/decache_student_scoring

CYB-164 https://jira.ets.berkeley.edu/jira/browse/CYB-164