logilab-mtconverter #5068 lynx transform leaves zombies around [validation pending]

Somehow there are cases where zombies of lynx are still around.

The library calls os.popen4 which uses popen2.Popen4 internally and the __del__ method is probably not called.

The code should use popen2.Popen4 explicitly or even better use subprocess.

btw there's a potential for deadlock as the code is writing a whole file to a pipe before reading the results. With subprocess one can use a tmpfile for stdout and avoir that.