couchdb commit-validation is triggered of "Ref updated"

The build bot is triggered on "Ref updated" changes in Gerrit. I'd prefer if it is only triggered on new patchsets. An example can be seen at [1] builds #247 and #248 (be quick as long as they are still there

It's been like that for a while but not always, hence I regard it as a regression.

[1] http://factory.couchbase.com/job/couchdb-gerrit-upr/