(spam-fetch-field-fast, spam-fetch-field-from-fast)

(spam-fetch-field-fast, spam-fetch-field-from-fast)
(spam-fetch-field-subject-fast)
(spam-fetch-field-message-id-fast, spam-generate-fake-headers)
(spam-fetch-article-header): new functions to deal with Gnus
internals for fast retrieval of article header data
(spam-initialize): put spam-find-spam in the gnus-summary-prepared-hook