We search through text/plain messages for URLs and make them clickable.
Here are some examples.

These should all have links over them:

http://home.netscape.com and http://home.netscape.com/, (and the
comma shouldn't be in the URL) "http://home.netscape.com:80/"
and <https://home.netscape.com> and mailto:jwz as well as
mailto:jwz%2Cterry, and mailto:jwz,terry, but note that the final
commas shouldn't be in the URLs.

http://host/some-random-image.map?300,200 should have both numbers
inside the link, and http://host/some-random.cgi?3,2,1, should
have all three numbers in the link, but not the trailing comma.
gopher://host/ blah blah blah. But http://host,other-junk should
stop before the comma, not include other junk in the URL.
news:some.group should work.

These should NOT have links over them:

mailto: shouldn't, since that's useless, as is news:, nor should
about: since that's a word that occurs at the end of a sentence a
lot. http: all by itself shouldn't have a link, neither should
gopher:, and "internal-gopher-binary" is a hackish internal image.
news:a shouldn't either, because it's short.
internal-external-reconnect sure shouldn't.

Ok! That should cover it.