Add gt to gte and lt to lte mutations

* I believe these are also good mutations as lt vs lte and gt vs gte
  differencies always will be observable from good specs and the
  developer will always be very sure he uses the right one.
Remove warning expectations

* Warnings do not disturb master output anymore as we redirect stderr of
  children to dev null. So the main reason for adding this feature is
  gone. BTW Its planned to capture the stderr of childrens later.
* Warning expectations do not work very well under zombification as line
  numbers change.
Use actor based parallelization