manual page editing almost done

* The code snippet in the netmap(4) examples should
  compile.  Haven't checked yet...

* A sentence in netmap(4) isn't finished.  Already
  asked Luigi for help.

* vale(4) needs more work from a developer eventually.
  Another possibility would be to merge the vale(4) bits
  into netmap(4) and add vale.4 to MLINKS.