Trying to diagnose Run.delete failure.

Observed in a log from 1.466.x:
… hudson.model.Run run
SEVERE: Failed to rotate log
java.io.IOException: …/builds/2013-… is in use
	at hudson.model.Run.delete(Run.java:1260)
	at hudson.model.AbstractBuild.delete(AbstractBuild.java:387)
	at hudson.tasks.LogRotator.perform(LogRotator.java:157)
	at hudson.model.Job.logRotate(Job.java:337)
	at hudson.model.Run.run(Run.java:1503)
	…