Add encoding to checkgroups processing

[eagle]

Add encoding specifications such as:

  # Output encoding for newsgroups file.
  /encoding/:utf-8

  # Incoming encodings in checkgroups.
  /encoding/:*:cp1252
  /encoding/:cn.*:gb18030
  /encoding/:fido.*:utf-8
  /encoding/:fr.*:iso-8859-15

and then update docheckgroups processing to use iconv to convert newsgroup descriptions to the output encoding before adding them to newsgroups.

[Julien ÉLIE]

There is also control/modules/newgroup.pl to update because encodings are also used there (new description or change of description of a newsgroup).

[Julien ÉLIE]

Descriptions SHOULD be in UTF-8, according to RFC 3977. Encoding specifications permit to comply with that.

[Julien ÉLIE]

(In [8315]) Add encoding to newgroup processing: controlchan now looks
for the charset and try to convert the description into
the local encoding.
Defaults are cp1252 for expected encodings (unless the charset
is properly set in the newgroup message, or control.ctl
dictates another charset) and utf-8 for the local encoding.

Add a few encoding exceptions to control.ctl.local.

(The man pages will be updated when checkgroups are also
processed the same way.)

see #4

[Julien ÉLIE]

(In [8375]) Add encodings to checkgroups processing: controlchan now looks
for the charset and try to convert the descriptions into
the local encoding.

Defaults are cp1252 for expected encodings (unless the charset
is properly set in the checkgroups message, or control.ctl
dictates another charset) and utf-8 for the local encoding.

close #4