use FileHandle and set autoflush on STDOUT since the new spam checking

use FileHandle and set autoflush on STDOUT since the new spam checking
is so fast the status reporting is now funky without autoflushing.

Document spam_check, spam_start_hook, spam_stop_hook.

My trick for defining is_spam() was broken and i never noticed because
i wasn't doing use strict in .mincspam; fix it with eval and also add
spam_start_hook and spam_stop_hook.

(kill_spam): Now call spam_start_hook(), save the list it returns, and
pass it to each spam_check() call (formerly known as is_spam()).  Also
pass it to spam_stop_hook() after processing all spam.  This allows
the spam processor to maintain state, and do other things like talk to
a co-process.