Gnus issues

[Dave Love]

Most of these things are shown up by compilation warnings, which it
seems people aren't getting attention.  (It seems more sane to bundle
these together rather than making individual reports.)

The use of `caddr' in gnus-diary.el should be replaced (or use CL).

gnus-picon.el uses `ignore-errors' without CL.

gnus.el needs to require message when compiling (for macro
`message-y-or-n-p').

imap.el uses `assert' incorrectly -- I guess the second arg should be
nil.

mailcap.el shouldn't define non-Lisp methods in
`mailcap-custom-mime-data'.  They should be picked up from the system
mailcap file, so that Emacs is consistent with other programs.
(That's especially relevant on Debian, where /etc/mailcap reflects the
programs actually installed.)  Then it's probably worth customizing
the variable.  [I should have sorted this out in the past...]

mml-smime.el needs to require cl when compiling.

nnml.el and nnfolder.el call assert and error incorrectly.

pop3.el shouldn't use nnheader-accept-process-output, so it can be
used outside Gnus.  It should probably define its own function as a
copy of that.  It can assume md5 is available, and I think its user
variables should be customized.  I think the bizarre `(if (>
(buffer-size)...' clauses in `pop3-retr' can safely be removed -- I've
run without them for some time.

rfc2047.el should autoload `mm-qp-or-base64'.

spam.el calls error incorrectly.

In mml.el, I think the second and third calls of `completing-read'
should have t for the fourth arg (REQUIRE-MATCH) since only the listed
completions are meaningful.  I tend to type `a RET' and expect it to
complete to `attachment', but it just makes the mml stuff in the
buffer invalid.