Update classchange controller for schema modifications.
Update class changes email for Spring HSSP 2014.
Fix students not checked in query.
Fixes class changes form

Request StudentRegistrations were being created with an end_date of
9999-01-01, which is incorrect for ExpirableModles. Removes this
assignment, so that end_date is correctly set as None when new
registrations are created.
Remove unused dblog code.

Looks like this app was designed to log errors in the database.  The last time
one was logged on esp.mit.edu was in 2010, so I don't think we're actually
using this functionality; let's kill it!

It was called in a few places:
* users.getTaughtClassesFromProgram attempted to log, but not raise, an error.
  This is really bad anyway so it now raises ESPError.
* the ESPError middleware attempted to save the error to the database after
  sending it to serverlog, but it was wrapped in a try-except block, and
  doesn't seem to have been happening.
* Some other navbar view imported, but did not use it.  That entire view seems
  to be unused, so I deleted it too.

I think in the long term we should probably improve our logging setup, possibly
involving a new-and-improved way of logging errors to the DB, but I don't think
we will actually want to build on this.

Solves #979.
Or maybe that navbar thing wasn't unused.

Bring it back and remove unused imports instead.
And remove something else that accidentally made it into the diff.
Adds a link for admins to give a medical bypass.

The link is on a student-facing page, but uses our magic css classes to hide it
from students.
Use Django's m2m_changed instead of our custom signals in depend_on_m2m

See: https://docs.djangoproject.com/en/dev/ref/signals/#m2m-changed
(introduced in Django 1.2)
Removes settings.LOG_FILE now that it is unused.
Merge branch 'main' into medical-bypass-link
Adds "grant medical bypass" to userview page.

It will only display if the module is enabled.
Fixes hasModule for nonexistent program.
Merge pull request #1222 from learning-unlimited/remove-dblog

Remove unused dblog code.
Merge pull request #1226 from learning-unlimited/medical-bypass-link

Adds a link for admins to give a medical bypass.
Merge pull request #1132 from learning-unlimited/classchanges_fixes

Classchanges fixes
Test removing and clearing in test_depend_on_m2m
Merge pull request #1235 from learning-unlimited/argcache-m2m-signals

Use Django's m2m_changed instead of our custom signals in depend_on_m2m
Merge branch 'main' into userview-availability
Check if availability module exists before displaying the link to it.