add build.buildid, sl.buildslaveid, and st.stepid

This required a lot of refactoring of old tests.  It also required
changing the automatic generation of source step names to generate
proper identifiers.
Merge branch '9/buildid-stepid-buildslaveid' of git://github.com/djmitche/buildbot into nine (PR #1018)

I re-addd status.build_started so that the try scheduler tests would
still work.
All resource types are now implemented, including buildrequests