On hosts where the `max_execution_time` can't be modified on the fly, set the time to wait based on the max_execution_time value.

This means we'll be waiting a shorter period of time before restarting the backup process.
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Use our more appropriate helper method
Merge branch 'master' into short-time-to-wait
Fix scenario where `$time_to_wait` could inadvernently be set to zero
Merge pull request #132 from humanmade/short-time-to-wait

Be more intelligent about the time we're waiting to report a backup process as dead