Thanks to your patch I now have --wrapper working, but I've spotted another
minor bug with it (which doesn't depend on whether args are passed to the
plugin). 

Basically the argument to --wrapper (the plugin/lib name) is used correctly,
but is then also treated as a URL to be fetched, which results in bogus errors
in hts-log.txt.

For example, if you run:
httrack --wrapper filename [other options] <http://example.com>

hts-log.txt shows:
14:54:29        Error:  "Unable to get server's address: No such file or
directory" (-5) after 2 retries at link filename/robots.txt (from
primary/primary)
14:54:29        Error:  "Unable to get server's address: No such file or
directory" (-5) after 2 retries at link filename/ (from primary/primary)

As I say, the wrapper plugin still works correctly so this is just a cosmetic
issue.