I have a small pile of stuff that ended up not being part of any significant change. There's the beginning of a document on the sixgill output format. There's a "simplfication" to the always-confusing BFS_upwards() stuff, which was necessary for a change that turned out to produce too many false positives, but I think the preparatory change is probably still better than what is there now? And finally, there's a pure refactoring that makes some direct data structure manipulation slightly easier to follow.

This was necessary for a change that I ended up not needing, but the main point of this patch is the commentary.

Backed out for causing hazard failures on rootAnalysis/analyze.py

Push with failures: https://treeherder.mozilla.org/jobs?repo=autoland&group_state=expanded&resultStatus=testfailed%2Cbusted%2Cexception&revision=2751ae76325c35a84d5781d1f507210cdbd72159&selectedTaskRun=M9SJI8SYQGaNn2E9N2IxfQ.0

Failure log: https://treeherder.mozilla.org/logviewer?job_id=412108269&repo=autoland

Backout link: https://hg.mozilla.org/integration/autoland/rev/79b976bdc2330d5df519bdd325b0a988fb02878e

Backout merged to central: https://hg.mozilla.org/mozilla-central/rev/79b976bdc233

https://hg.mozilla.org/mozilla-central/rev/3b3ebbf22ea9
https://hg.mozilla.org/mozilla-central/rev/d5babfab79d6
https://hg.mozilla.org/mozilla-central/rev/7fb2661a3faf