Add patch to mute "RSA_verify failed" messages

bind 9.9.2 has a bug that makes it spam syslog with messages like this
"named[74116]: general: warning: RSA_verify failed"

This change includes a small patch to mute those messages, as
recommended by ISC in
http://comments.gmane.org/gmane.network.dns.bind.user/47382 - and
enables it by default.

This problem should be fixed in bind 9.9.3 so this patch is only a
temporary fix.