Keep comments in capa XML from causing failures

Comments (and processing instructions!) are handled oddly in lxml.
This change will keep them from causing failures.  They will be omitted
from the HTML generated, which is fine, since they aren't needed there.
A test that our XML-comments fix works.
Check extension rather than mimetype
Merge pull request #819 from edx/jkarni/hotfix/gzip-mimetype

Check extension rather than mimetype
Merge pull request #816 from edx/hotfix/xml-parsing

Hotfix/xml parsing
Skip acceptance test DB migrations if the DB already exists and running fasttest_acceptance
add pyparsing explicitly to sandbox requirements
add pyparsing to edx requirements
Fix for acceptance test static file issue
Fix multiple video bug
Merge pull request #849 from edx/will/acceptance-test-static-files

Fix for acceptance test static file issue
Merge pull request #848 from edx/fix/adam/add-edge-reqs

Fix/adam/add edge reqs
fix pep8 and pylint errors

Conflicts:
	cms/djangoapps/contentstore/views/course.py
	common/lib/xmodule/xmodule/tests/test_combined_open_ended.py
	lms/envs/common.py
Merge pull request #837 from edx/will/faster-acceptance-test-startup

Skip migrations if running acceptance in fasttest mode
Merge pull request #851 from edx/hotfix/release-multiple-video-bug

Hotfix/release multiple video bug
resolve merge conflict with hotfix branch
Cleanup bulk email app
Merge pull request #856 from edx/adam/merge-conflicts

Adam/merge conflicts
Merge pull request #853 from edx/fix/adam/pylint-pep8

fix pep8 and pylint errors
Merge pull request #855 from edx/sarina/bulkemail-violations

Cleanup bulk email app