Log Message:
Update to 7.16.

* New commands:
  + vm-visit-imap-folder
  + vm-visit-imap-folder-other-window
  + vm-visit-imap-folder-other-frame
  + vm-save-message-to-imap-folder
* New variables:
  + vm-imap-server-list
* vm-primary-inbox can now be a POP or IMAP mailbox specification.
* vm-mime-set-xxx-parameter: use the parameter name passed in
  instead of assuming the name is "charset".  The only calls to
  this function passed in "charset" as the name, so this bug
  wasn't affecting anything.
* vm-decode-mime-encoded-words: do charset conversion if needed.
  Forgot to add this back when vm-mime-charset-converter-alist
  was added.
* vm-send-mail-and-exit -> vm-mail-send-and-exit in vm-user-agent
  definition.
* vm-mail-send-and-exit: dropped first arg requirement since the
  argument isn't used anyway.
* compute POP cache filenames based on the POP mailbox spec with
  the access method as "pop" and the authentication method and
  port as asterisks.  This prevents visiting the wrong file if
  the user starts accessing a POP mailbox through a different
  port or using a different access or authentication method.
  Automatically migrate the old cache files to the new scheme as
  we go.
* fixed convert -page typos.
* vm-set-redistributed-flag: fourth arg of vm-set-xxx-flag
  call corrected to be vm-set-redistributed-flag instead of
  vm-set-forwarded-flag.
* IMAP BYE responses are always untagged; changed code to match.