Fix FTP error code scraping
Substitute old and removed module names

* “sre” seems to be an old name for the “re” module
* “whrandom” deprecated since Python 2.0 and removed from 2.5; assuming
  random.randint() is equivalent
* parser.ast2list() is gone from Python 3, but seems to have been equivalent
  to parser.st2list()
Missing string formatting