Add a version of NwaToWPdsCalls that takes the output WPDS by reference.
Add Nwa::poststarViaFwpds to perform poststar by converting the nwa to an FWPDS

Beware that FWPDS are no reentrant right now. This means that if you already
have some fwpds lying around then the two fwpds objects might interfare.
Merge branch 'master' into nwa_detensor
The merge had broken the unit-test build due to semantically incorrect merge. Fixed.