Merge pull request #392 from dzhuang/course_specific_language

course/migrations/0110_add_force_lang_field_to_course.py

course/models.py

course/utils.py

course/versioning.py

course/views.py

local_settings.example.py

relate/checks.py

tests/base_test_mixins.py

tests/test_checks.py

tests/test_misc.py

tests/test_utils.py

tests/test_views.py