Trivial Description
In HBASE-4347 I factored some code from Put/Delete/Append in Mutation.
In a discussion with a co-worker I noticed that Put/Delete/Append still implement the Row interface, but Mutation does not.
In a trivial change I would like to move that interface up to Mutation, along with changing HTable.batch(List<Row>) to HTable.batch(List<? extends Row>) (HConnection.processBatch takes List<? extends Row> already anyway), so that HTable.batch can be used with a list of Mutations.