Make better effort at killing Heritrix if calling Process.destroy fails

After the fix of bug 1711 the Harvest Controller vil commit suicide if it fails to kill Heritrix. This prevents the undesirable effects described in that bug but it does also lead to a situation where no more jobs are accepted by that harvester.
It is probably possible to make a better effort at killing the process e.g. sending a kill signal in a system dependant way (kill on linux taskkill on windows) if we can somehow recognise the process.