Please add StartCom Root CA Certificate to cacerts.pem
Problem
StartCom offers free Class 1 XMPP server certificates (see http://www.startssl.com and http://blog.xmpp.org/index.php/2009/09/ca-updates/). Gajim shows a certificate error message when connecting to a server using such a certificate.
Analysis
The appropriate Root CA Certificate is missing in Gajim's cacert.pem (it only contains an older one from StartCom).
Enhancement recommendation
Please add StartCom's Root CA Certificate: https://www.startssl.com/certs/ca.pem