mail/spamassassin: Update 3.4.6 --> 4.0.0
The release announcement can be found at
https://svn.apache.org/repos/asf/spamassassin/trunk/build/announcements/\
4.0.0.txt.
A list of detailed changes can be found at
https://svn.apache.org/repos/asf/spamassassin/trunk/Changes.