Gets the index of the specified #GMimeCertificate inside the #GMimeCertificateList.
a #GMimeCertificate
the index of the requested #GMimeCertificate within the #GMimeCertificateList or %-1 if it is not contained within the #GMimeCertificateList.
Gets the index of the specified #GMimeCertificate inside the #GMimeCertificateList.