perf impact on nightly release automation move

If you care about the behavior of the Firefox perf test machines, please check out my post moving Mozilla1.8 tinderboxes to Buildbot - perf impact in the newsgroup.

The big question is whether we can move to a model where we only build on checkin rather than continuously. This change would mean faster build turnaround times for developers, and a reduced load on build machines. It also means that the perf machines cycle less often. Currently, there's no way to disambiguate the start time of the run versus the latest revision in the build (for CVS, revision in this sense is branch+timestamp), Tinderbox and graph servers all expect build and perf run to be the same thing.

In case you're wondering why I'm worried about the Mozilla1.8 tree, if all goes well with this rollout we'll want to do it this way on Firefox tree as well; the Mozilla1.8 branch is stable and already on release automation, so we think it makes sense to start there first.