Build fails on Travis-CI with "Comparison method violates its general contract!"

[avernet]

Full error message:

[junit] Comparison method violates its general contract!
[junit] java.lang.IllegalArgumentException: Comparison method violates its general contract!
[junit]     at java.util.TimSort.mergeLo(TimSort.java:747)
[junit]     at java.util.TimSort.mergeAt(TimSort.java:483)
[junit]     at java.util.TimSort.mergeCollapse(TimSort.java:410)
[junit]     at java.util.TimSort.sort(TimSort.java:214)
[junit]     at java.util.TimSort.sort(TimSort.java:173)
[junit]     at java.util.Arrays.sort(Arrays.java:659)
[junit]     at java.lang.reflect.Constructor.newInstance(Constructor.java:525)

[avernet]

This was caused to a JDK 7 bug. We had this on Travis-CI, which at the time was running:

Java(TM) SE Runtime Environment (build 1.7.0_17-b02)
Java HotSpot(TM) 64-Bit Server VM (build 23.7-b01, mixed mode)

I couldn't reproduce this locally on OS X with exactly the same version of Java. Setting the java.util.Arrays.useLegacyMergeSort system property to true, as suggested in this Stack Overflow answer, gets us around the problem.