[Buildbot] #3014: Add a migrator that reverts db version 40

[Buildbot trac]

#3014: Add a migrator that reverts db version 40
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Reporter:  Ben       |       Owner:
    Type:  defect    |      Status:  closed
Priority:  critical  |   Milestone:  0.9.0
 Version:  master    |  Resolution:  fixed
Keywords:            |
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Changes (by dustin):

 * status:  new => closed
 * resolution:   => fixed


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Ticket URL: <http://trac.buildbot.net/ticket/3014#comment:6>
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