one-line-per-sentence policy for the section to update

* to make it easier to see the differences
clarify a bit the difference between master- and slave-side source steps

* emphasise the difference between them
* since master-side steps are recommended move them up in the examples
* slave-steps are deprecated and will be removed in 0.9
* emphasise that the next section is about master-side steps
factor out integration-style step testing support
add an integration test that renders a new-style step
Tickle #2934
Fix checkLogfiles to not fail with new style steps
Fix cross-site scripting in status_json by specifying nosniff and app/json content
Merge pull request #1254 from djmitche/bug2934

Test for and fix new-style step assertions triggered by Buildbot code

Fixes ticket:2934
Merge pull request #1258 from wmswms/eight

Bugfix 2943: Fix cross-site scripting in status_json by specifying nosniff and app/js...

Fixes ticket:2943
Merge sa2ajj/buildbot:new-old-source-steps (PR #1252)