write xmlrpc function updateSeverity that is to be contributed to the upstream.
Please refer to the following url for details on Bugzilla::RPC 2.18 functions mapped to upstream Bugzilla::WebService and for 2.18 xmlrpc functions sorted by percentage of calls: https://engineering.redhat.com/trac/bugzilla-3.0-rh/wiki/XmlrpcCrossComparison#a2.18xmlrpcfunctionssortedbypercentageofcalls
This feature is included now in Milestone 2. Any bugs found with this feature
should be file as a new report and set to block the 3.2 final release tracker.