[Buildbot] #3490: re-enable foreign keys for sqlite

[Buildbot trac]

#3490: re-enable foreign keys for sqlite
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Reporter:  tardyp       |      Owner:
    Type:  enhancement  |     Status:  new
Priority:  major        |  Milestone:  undecided
 Version:  master       |   Keywords:
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 Some people reported issues since I enabled foreign keys in sqlite.

 symptom is that no build is scheduled anymore.

 rootcause is theat in scheduler/base.py getChangeClassifications() always
 return []

 I believe this might be because sqlite might FK prevent insertion of
 changes in scheduler/change table.

 I prefer to temporarily disable fk in order to unblock mainline, as I
 think this might be tricky to really fix

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Ticket URL: <http://trac.buildbot.net/ticket/3490>
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