We should keep the jar naming consistent between the builds. Could we just add this?

```
jarName in assembly <<= version map { v => "spark-assembly-" + v + "-hadoop" + hadoopVersion + ".jar" },
```

You might be able to just do `System.getProperty("hadoop.version"))`, or if there are some ordering issues between this code and `backwardsCompatiblity`, you could factor this out into a function.