Modifications to instructor dashboard - enrollment tab:

- Remove single enrollment/unenrollment
- Make unenrollment work with multi-email listbox.
- Provide checkbox for auto-enroll on activate if user not yet signed
up.
- Enroll student when activating if auto-enroll flag set.
Merge branch 'master' of github.com:MITx/mitx into feature-dcadams-usermanagement
Some cleanup.
Merge branch 'master' of github.com:MITx/mitx into feature-dcadams-usermanagement
Merge branch 'master' of github.com:MITx/mitx into feature-dcadams-usermanagement
Fix pep8 violations.
Merge branch 'master' of github.com:edx/mitx into feature-dcadams-usermanagement
Commit just to get Jenkins to rerun.
Merge branch 'master' of github.com:edx/mitx into feature-dcadams-usermanagement
Merge branch 'master' of github.com:edx/mitx into feature-dcadams-usermanagement
Merge branch 'master' of github.com:edx/edx-platform into feature-dcadams-usermanagement
Takes care of Victor's comments on the PR.

Note, the students_lc list is used in _do_enroll_students when overload
= True so it needs to be left in.
Merge branch 'master' of github.com:edx/edx-platform into feature-dcadams-usermanagement
Merge of master to get Jenkins running.
Added tests for Limited Attempt Problems and Showing the Answer
Sped up some Lettuce Tests
Sped up tab lettuce test
Accidently left in a set_trace and forgot to include files
Consolidated coverage report generation into one rake command.
Added diff coverage reports using diff-coverage tool.
Added requirement for pip>=1.3