Update java.util.Arrays.sort to the clean implem in Scala 2.11.7

[sjrd]

Quoting @adriaanm from #1746 (comment):

Hey @sjrd, @nicolasstucki, @gzm0: it looks like you copy/pasted code from 2.11.5 which was copy/pasted from the forbidden fruit, so please update to the ones in 2.11.7 ASAP: scala/scala#4557

We must update our implementations of java.util.Arrays.sort to the clean ones in Scala 2.11.7.