Changes to SeaMonkey nightlies and tinderbox waterfalls

As discussed and decided in the last SeaMonkey Status Meeting, I've started to move SeaMonkey to the new buildbot configurations that have been in the testing phase for a while now and will open the possibilities for doing builds based on mozilla-central soon.

The following changes are made that you should be aware of:

Phase I (done yesterday, first nightlies from today):

• The nightlies in latest-comm-1.9.1 are the official ones now.
• FTP has latest-comm-central and latest-trunk symlinked to latest-comm-1.9.1 for the first part of the transition.
• Those are static builds with reduced build size and hopefully better performance.
• Dependent builds ("build" columns, "hourlies") continue to be shared builds.
• Linux has a "leak test build" column that runs debug builds.
• Nightlies and dependent builds are being run on x86_64 Linux, even though this should still not be considered a tier-1 platform and has no L10n builds.
• Localized nightlies are in latest-comm-1.9.1-l10n and built with the "L10n merge" tooling that injects en-US for missing strings, eliminating most cases of the "yellow screen of death".
• The SeaMonkey tinderbox waterfall page has those buildbots reporting as columns containing "comm-1.9.1" in their names.
• Due to ongoing slight instabilities in the 10.5 VMs, the old "comm-central" 10.4 unit test machine stays up there as well.
• All other comm-central builds disappear from the scene.
• For localizers, the comm-1.9.1 builds on their Mozilla-l10n-* waterfall pages are the relevant reference.
• All VMs on the same platform run in generic pools, so that any of the machines can do any dependent build, nightly, L10n repackaging or unit test run, the buildbot master hands those jobs on a "first come, first serve" basis to the available slaves.

Phase II (once bugs 502031 and 502033 are solved):

• Builds with mozilla-central are set up in addition, uploading nightlies to a latest-comm-central-trunk directory.
• A version number of "2.1a1pre" is used there for now, there's no definitive decision on what version the next SeaMonkey will be yet though, this is the lowest possible version to use atm.
• FTP symlinks for latest-comm-central and latest-trunk are removed.
• The comm-1.9.1 builds are switched to report to a new SeaMonkey2.0 tinderbox waterfall page (as well as the 10.4 tests).
• The comm-central-trunk builds report to the SeaMonkey page.
• No unit test builds will be activated for comm-central-trunk while we don't have all the machines we need in the pools (due to Parallels network problems).
• L10n builds for comm-central-trunk use l10n-central work and also report to the Mozilla-l10n-* tinderbox waterfalls, dashboard for this might only come up some time later.

Phase III (once bug 493321 is solved):

• Unit tests for comm-central-trunk are turned on.
• A few other incremental improvements can be thought of when Phase II is completed, such as running packaged tests, AUS for L10n, etc. but all those can be done individually, step by step, then.
• Once 10.5 Mac VMs are completely stable and not intermittently crashing because of Parallels issues, we'll turn off the 10.4 unit test machine and hand it back to Mozilla IT.

I hope this whole transition works well for everybody. It was a bumpy ride and a good amount of work to get this all up, but it largely reduced the amount of maintenance needed and makes us share more buildbot code with Firefox and Thunderbird already now and even more once this all is completed.