Proposed patch for #2589 to guard against content spoofing.
Remove assert from subscribeConsumer

This method is used by the WebStatus, and thus necessary (even for
new-style steps) in eight.
Catch a specific exception
Update release notes for #2589
Fix one more missing exception
Merge pull request #1249 from djmitche/subscribeConsumer-assert

Remove assert from subscribeConsumer
Merge pull request #1244 from wmswms/eight

Guard against content spoofing.

Fixes ticket:2589
apply one-sentence-per-line rule to the changed section
update documentation for GitHub change hook

* misc syntax, wording and cosmetic changes
* move mention of standalone server to the beginning of the section
* fix link to the GitHub tutorial for adding webhooks
* make list of parameters of GitHub webhook and their correpsonding
  values explicit

Fixes ticket:2938
Merge sa2ajj/buildbot:bugfix-2938 (PR #1253)