[Merge] lp:~jamesodhunt/upstart/log_clear_unflushed-assert-fix into lp:upstart

[Stéphane Graber]

Review: Approve

I think that looks good.

Sadly there's no easy way for me to reproduce the initial bug (never happened again) so I can't say for sure that this fixes it.
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https://code.launchpad.net/~jamesodhunt/upstart/log_clear_unflushed-assert-fix/+merge/165637
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