[VM] IMAP cache

[Johan Vromans]

Hi,

From the docs:

  When you visit an IMAP folder, VM will download copies of the
  messages that it finds there for you to read.  These messages are saved
  locally in a folder on the disk, in the directory specified by
  `vm-imap-folder-cache-directory' (or `vm-folder-directory' if the
  former is not defined).

It seems that VM maintains the local copies in a single mailbox file, which
quickly tend to grow very big, hence slow.

Is it possible to maintain the local copies in a maildir style format?

-- Johan