New patch. Adds methods to NamedList: public methods removeAll and removeArgs, private method killAll. Removes the oneOrMany method from FieldMutatingUpdateProcessorFactory. Adds tests for new methods, improves one existing test. I am seeing a replication stress test failure, but I don't think it's related to these changes. The patch has a conflict on branch_4x, so I haven't done any testing there yet.
All this so I can use removeArgs in my own custom update processors!
Please let me know if there is any objection to committing this after making sure branch_4x is good.