Make wl-highlight-message use the citation depth for choosing the face.

Rather than using a stateful algorithm for choosing arbitrary but
distinct faces for the various citation prefixes in the message,
this uses the citation depth for plain citations and an arbitrary
hash of the attribution name for SC-style attributions.
Implement draft highlighting using jit-lock-mode.

This uses Emacs' 21 native highlighting mechanism, and is enabled
by default if available.
elmo-util.el (elmo-max-of-list): Refactored.
elmo-util.el (elmo-max-of-list, elmo-cache-get-path-subr, elmo-warning): Explicit function's symbols.
elmo-util.el (elmo-max-of-list): Fix the last change for the case argument is nil.
Improve performance of uniquifying large list of sortable numbers.
wl-summary.el (wl-summary-default-subject-filter): Minor refactoring.
Keep multiple parent Message-IDs in msgdb.
elmo-util.el (elmo-list-diff): Simplified.  Sort each element of return value.
wl-summary.el (wl-summary-insert-thread): Report progress.
Merged from upstream.
Don't recompute in-header in wl-draft-default-jit-highlight.

This was wrong, since point may have changed by then, and caused
mis-highlighting of the first line if it was quoted.
Merge branch 'master' of git://github.com/wanderlust/wanderlust
elmo-imap4.el (elmo-imap4-setup-send-buffer): Fix typo.  Bind inhibit-eol-conversion to nil before code conversion.
elmo-pop3.el (elmo-pop3-read-body): Fix trying to access buffer local variable from another buffer.
Check references field's value by user.
Update elmo-file so it works with modern versions of the file utility.

This uses "file -i" instead of "file -m".  Additionally, if file is kind
enough to provide a charset, we trust the result and avoid decoding and
recoding the data multiple times.
Fix typo in elmo-map-folder-list-message-locations (elmo-file-folder).

Due to a missing expand-file-name, we were including subdirectories,
which caused searches to fail.
Add the comment for old msgdb.
Fix digest flag search for IMAP and NNTP folders.