Update CHANGES.txt for 0.98.3RC1
HBASE-11234 FastDiffDeltaEncoder#getFirstKeyInBlock returns wrong result
HBASE-11255 Negative request num in region load (Liu Shaohui)
HBASE-11118 non environment variable solution for "IllegalAccessError: class com.google.protobuf.ZeroCopyLiteralByteString cannot access its superclass com.google.protobuf.LiteralByteString"