* gnus-cite.el (gnus-cite-face-list): Set the value of

* gnus-cite.el (gnus-cite-face-list): Set the value of
 gnus-message-max-citation-depth.
(gnus-message-max-citation-depth): Use defvar rather than defconst.
(gnus-message-cite-prefix-regexp): New variable.
(gnus-message-search-citation-line): Use it;
 protect against long citation prefix;
 fill match data with nil rather than 0 for XEmacs;
 set the 0th match data for Emacs.
(gnus-message-citation-keywords): Set LAXMATCH flag in every HIGHLIGHT.
(gnus-message-add-citation-keywords): Append keywords rather than prepending;
 emulate font-lock-add-keywords if it is not available.
(gnus-message-remove-citation-keywords): Emulate font-lock-remove-keywords if
 it is not available.

* gnus-msg.el (gnus-message-highlight-citation): Default to t.

* message.el (message-cite-prefix-regexp): Set the value of
 gnus-message-cite-prefix-regexp.