Fix #1171: Split: Sometimes remove leading empty match

The conditions were determined experimentally since the JavaDoc is
note precise enough.
Uh, oh... I get a different result with:
```
Welcome to Scala version 2.11.1 (Java HotSpot(TM) 64-Bit Server VM, Java 1.7.0_45).
```

What is your JVM/ Scala version?