Git: Don't break when there is a file called `FETCH_HEAD`.

We want to refer to the branch FETCH_HEAD, not a file, so let git know that.
(Reported by loul2 on #buildbot)
GitPoller: Disambiguate versions from file names.

The revision that we use for GitPoller are probably never going to exists
as files, but it doesn't cost us anything to avoid issues here.
Update pyflakes project url.  divmod.org says it's offline, and to use launchpad instead.
Fix BuildStatus.getAllGotRevisions to properly handle vcs that use int.

Fixes #2388, #2380.
Raise ImportError instead of exiting, if buildbot.test can't be imported.

This apparently causes issue with 'pydoc -k', and is in general not nice.
Trial still fails with a sensible error message.
Make pyflakes happy.
SetPropertiesFromEnv: Use properties from slave, rather than set on master.

The old implementation incorrectly used the set of environment variables set
on the master, rather than those retrieved from the slave, when setting properties.

Fixes #2393.
SetPropertiesFromEnv: Properties from the slave will always be strings.

So the tests should use strings there too.
SetPropertiesFromEnv: Log property changes.

Fixes #2361.
Merge branch 'log-env' into buildbot-0.8.7
Make sphinx happy.
Git: Fix cloning with default branch.

``git`` doesn't like it when we specify the default ``HEAD`` to ``git-clone``
using ``--branch``.
Git: Document that not specifying a branch gets the default remote branch.

This has been the behaviour since 0.8.6, so fix the documentation to match.

Refs #1773.
add relnotes about no longer supporting multi-argument addStep
proper link to old versions' release notes
Fix Mercurial to update to specified branch

With inrepo branches the Mercurial master side source steps
did not update to the specified branch when no revision was specified.
Merge branch 'mercurialbranch' of git://github.com/pepsiman/buildbot into buildbot-0.8.7
Merge branch 'git-HEAD-clone' into buildbot-0.8.7
Merge branch 'git-disamiguate' into buildbot-0.8.7
start: Don't fork when not daemonizing.

The reason not to fork, is to make it easier for process monitors
to manage. Forking subverts that.