Update HISTORY.md, fix unity_test failure (facebook#4479)

Summary:
Follow-up to facebook#4432.
Pull Request resolved: facebook#4479

Differential Revision: D10304151

Pulled By: abhimadan

fbshipit-source-id: 3608b95c324702ca26791f95cb26dae1d49efbe7

HISTORY.md

@@ -5,6 +5,7 @@
 
 ### Bug Fixes
 * Fix corner case where a write group leader blocked due to write stall blocks other writers in queue with WriteOptions::no_slowdown set.
+* Fix in-memory range tombstone truncation to avoid erroneously covering newer keys at a lower level, and include range tombstones in compacted files whose largest key is the range tombstone's start key.
 
 ## 5.17.0 (10/05/2018)
 ### Public API Change

db/range_del_aggregator.cc

@@ -10,8 +10,6 @@
 
 namespace rocksdb {
 
-namespace {
-
 struct TombstoneStartKeyComparator {
   explicit TombstoneStartKeyComparator(const InternalKeyComparator* c)
       : cmp(c) {}
@@ -36,8 +34,6 @@ struct ParsedInternalKeyComparator {
   const InternalKeyComparator* cmp;
 };
 
-}  // namespace
-
 // An UncollapsedRangeDelMap is quick to create but slow to answer ShouldDelete
 // queries.
 class UncollapsedRangeDelMap : public RangeDelMap {