Posting with mime attachment?

I use slrn for mailing lists via gmane.org, and I occasionally need to
post an article with an attachment (typically a patch-file).  How does
one attach a file to a post using slrn?

Is there a command-line utility I can use to easily prepare a
multipart/mixed message?

-- 
Grant Edwards               grant.b.edwards        Yow! Thousands of days of
                                  at               civilians ... have produced
                              gmail.com            a ... feeling for the
                                                   aesthetic modules --


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