(imap-cram-md5-auth): Specify the 4th arg to `md5' as `binary' if possible.

(imap-cram-md5-auth): Specify the 4th arg to `md5' as `binary' if possible.
(imap-log): Default to nil (synched with pgnus 0.99).
(base64-decode-string): Autoload "mel" instead of "base64".
(md5): Autoload "md5" without `eval-and-compile'.
(cl): Enclose the requiring procedure with `eval-when-compile' instead of
`eval-and-compile'.