Patch from Melchior Franz:

Patch from Melchior Franz:

My last patch fixed the initialization problem only for the main branch, but
ignored the _MWERKS_ branch.
- merged the branches, only the loop head needs different treatment;
- don't access n.type before it is initialized (valgrind complaint)
- created a constructor; the operator>> wouldn't have initialized all
  variables in case of a broken default.nav.gz entry, so we would have
  got a mixture of the broken one and the previous one; in case of
  the first entry, that would have made nice random values ... ;-)
- move the automatic FGNav variable into the loop, so that the gets
  cleanly constructed for every database entry.
- commented out the frequency min/max exploration, which isn't used at all
- updated the commented out debug output statements, which were simply
  copied over from the nav* files, but never adapted (I needed them :-)