Fix Eclipse compiler warnings

I've split the various fixes into separate commits to illustrate why/how I fixed certain warnings.
I tried it, both `serialver` and Eclipse generate the same `serialVersionUID`:

### serialver

```sh
$ serialver -classpath junit-4.12.jar org.junit.internal.runners.rules.ValidationError 
org.junit.internal.runners.rules.ValidationError:    static final long serialVersionUID = 3176511008672645574L;
```

### Eclipse

```java
private static final long serialVersionUID = 3176511008672645574L;
```

Thus, I would like to fix the compiler warning with this explicit `serialVersionUID`.