examples/ct: use Certificate.Equal not ==
examples/ct: use Certificate.Equal not ==

Plain equality operator will fail to spot some equal certs,
because Certificate.PublicKey is an interface{}

google/certificate-transparency-go,daviddrysdale/certificate-transparency-go,daviddrysdale/certificate-transparency-go,google/certificate-transparency-go,RJPercival/certificate-transparency-go,daviddrysdale/certificate-transparency-go,RJPercival/certificate-transparency-go,google/certificate-transparency-go,RJPercival/certificate-transparency-go