changeHorizon set too soon

[dustin]

2011-06-02 01:48:00+0200 [-] Unhandled Error
        Traceback (most recent call last):
          File "/home/buildbot/metabuildbot/src/master/buildbot/master.py", line 189, in loadTheConfigFile
            d = self.loadConfig(f)
          File "/home/buildbot/metabuildbot/src/master/buildbot/master.py", line 535, in loadConfig
            d.addCallback(do_load)
          File "/home/buildbot/sandbox/lib/python2.6/site-packages/twisted/internet/defer.py", line 297, in addCallback
            callbackKeywords=kw)
          File "/home/buildbot/sandbox/lib/python2.6/site-packages/twisted/internet/defer.py", line 286, in addCallbacks
            self._runCallbacks()
        --- <exception caught here> ---
          File "/home/buildbot/sandbox/lib/python2.6/site-packages/twisted/internet/defer.py", line 542, in _runCallbacks
            current.result = callback(current.result, *args, **kw)
          File "/home/buildbot/metabuildbot/src/master/buildbot/master.py", line 325, in do_load
            self.db.changeHorizon = changeHorizon
        exceptions.AttributeError: 'NoneType' object has no attribute 'changeHorizon'

[Dustin J. Mitchell]

Store configuration values in master.config

This immediately fixes #1975, but opens the door to storing a lot more configuration here.

Changeset: 36617a8ad1a23e75448991e79616074ad8a96378