* Changed unicode test cases to ascii encoding
* Removed 'stanford' hardcoding in TOS logic in lieu of
  'SHIB_DISABLE_TOS' MIT_FEATURES flag
* made 'external_auth' always an installed_app in lms
* log.exception changd to log.error where appropriate

But: did not change skipping tests to changing settings, for
reasons stated here:
https://github.com/edx/edx-platform/pull/67#issuecomment-19790330

As stipulated by Stanford's office of general counsel

By linking the users

Highlights:
* The url '/shib-login/' interfaces with apache/mod_shib via
  request.META to handle shibboleth login and registrations
* Courses can designate 'enrollment_domains' to limit enrollment
  to users with a linked ExternalAuthMap verified by a particular
  identity provider
* Tests
* Logging

 Changes to be committed:

	new file:   common/djangoapps/external_auth/migrations/0001_initial.py
	new file:   common/djangoapps/external_auth/migrations/__init__.py
	new file:   common/djangoapps/external_auth/tests/test_shib.py
	modified:   common/djangoapps/external_auth/views.py
	modified:   common/djangoapps/student/views.py
	modified:   common/lib/xmodule/xmodule/course_module.py
	modified:   lms/djangoapps/courseware/access.py
	modified:   lms/djangoapps/courseware/tests/test_access.py
	modified:   lms/envs/common.py
	modified:   lms/envs/dev.py
	modified:   lms/envs/test.py
	modified:   lms/templates/courseware/course_about.html
	modified:   lms/templates/dashboard.html
	modified:   lms/templates/extauth_failure.html
	modified:   lms/templates/navigation.html
	modified:   lms/templates/register.html
	modified:   lms/templates/signup_modal.html
	modified:   lms/urls.py
	renamed:    lms/wsgi_apache.py -> lms/wsgi_apache_lms.py

wsgi_apache.py passes an apache env variable for SERVICE_VARIANT
to the os environment, where it's normally set when we use gunicorn

Fix a bug in diff-cover

Feature/brian/regrade celery 2

Cherry pick change to url matching regular expression. Fixes LMS-37

remove assets.js from the PIPELINE_JS since it seems to cause that file ...

When changing variable names for code review critique, accidental cut/paste prevented intended behavior.

Fix a few remaining tz naive dates

need to import os

Rename fields in CourseTaskLog, including a task_key column for indexing.  Use 'rescore' instead of 'regrade'.  Clean up task submission.

Add tracking calls to reset (and delete).  Add tests for delete.  Remove sleep statement used for manual testing.

Define MITX_FEATURES['ENABLE_COURSE_BACKGROUND_TASKS'] to allow background tasks to be removed from instructor dash.