* lisp/gnus/mm-util.el (mm-codepage-iso-8859-list, mm-codepage-ibm-list): New
variables.
(mm-setup-codepage-iso-8859, mm-setup-codepage-ibm): New functions.
(mm-charset-synonym-alist): Move some entries to
mm-codepage-iso-8859-list.
(mm-charset-synonym-alist, mm-charset-override-alist): Add
iso-8859-8/windows-1255 and iso-8859-9/windows-1254.