mergeChunks fails with empty error message if merging chunks that were moved.

This issue was originally reported in Google Groups: https://groups.google.com/forum/#!topic/mongodb-user/cN6Etk06S4g

The error shown in the mongo shell is:

{ "ok" : 0, "errmsg" : "" }

The error shown in the log is:

BadValue: chunk operation commit failed: version 3|2||57eb2b8706ec6135f8ef76eb doesn't exist in namespacetest.test. Unable to save chunk ops.

The cause for the error is that the version mentioned in the logs doesn't exist in the chunks collection in the config database. It was looking for version (3,2), while the last entry in the chunks collection is version (3,1).

Jstest to reproduce the issue is attached.