- override MESSAGE with one that also tells people to preload
pthread (you can do this via login.conf and rc scripts), text was
borrowed from ports/mail/zarafa.
Note! Without this, if you use pecl-imagick with the httpd from base,
the web server will fail to start:
/usr/sbin/httpd:/usr/local/lib/libMagickCore.so.2.0: undefined symbol 'pthread_mutexattr_init'
Users of Horde/IMP will need to take care of this.
Problem found the hard way by viq.