WrapTask does not fill in manifest

Same issue as #265, but for WrapTask.java:

```
            wrapper.calcManifest();
            if (wrapper.isOk()) {
```

should be:

```
            java.util.jar.Manifest mf = wrapper.calcManifest();
            if (wrapper.isOk()) {
                wrapper.getJar().setManifest(mf);
```

otherwise the bndwrap ant task produces none of the OSGi headers in the manifest.
