Show name of force builders.
Support for version from old versions of git.
Get version from proper directory, for checked out versions.
Fix authz for use with twisted's distrib proxy.

The PB remote proxy for addCookie only accepts two positional arguments, and
the rest must be keyword arguments.
Don't accept empty changes in PBChangeSource.

twisted currently depends on empty changes being dropped.
Disable deprecation warnings related to magic-__new__.

The existing custom steps don't use addFactoryArguments, so don't
support new-style factory usage. But with the magic-__new__ branch,
they should just work. In the mean-time, hide the useless warning.
Only set .fileIsImportant if it is not null.

This breaks subclassing schedulers that implement fileIsImportant as method.
Add test to make sure fileIsImporant declared in a subclass works.
Mark todo, failing tests caused by local hacks.
Port force-build refactorization from 0.8.7.
Allow forcing on multiple builders at once.

The web status currently does this by forcing multiple times, once for each builder,
creating a separate buildset for each. Instead, teach ForceScheduler to support
starting multiple builders in a single buildset, and refactor the webstatus code to
support that.
Some hack-ish code to support forcing via pb.
Add a link to the buildslave page in the missing slave email.

Fixes #344.
Rebuild tip of branch, when rebuilding branch build.

Fixes #1060920.