Fix RecordIn and RecordDrop stats

Summary:
1. fix possible overflow of the two stats by using uint64_t
2. use a similar source of data to calculate RecordDrop. Previous one is not correct.

Test Plan: See outputs of db_bench settings, and the results look reasonable

Reviewers: MarkCallaghan, ljin, igor

Reviewed By: igor

Subscribers: rven, leveldb, yhchiang, dhruba

Differential Revision: https://reviews.facebook.net/D28155
Add db_bench option --report_file_operations

Summary: Add db_bench option --report_file_operations

Test Plan:
./db_bench --report_file_operations
Observe outputs on # of file operations

Reviewers: ljin, MarkCallaghan, sdong

Reviewed By: sdong

Subscribers: yhchiang, rven, igor, dhruba

Differential Revision: https://reviews.facebook.net/D27945
suppress JDK8 errors for #385
Make sure WAL is synced for DB::Write() if write batch is empty

Summary: This patch makes it a contract that if an empty write batch is passed to DB::Write() and WriteOptions.sync = true, fsync is called to WAL.

Test Plan: A new unit test

Reviewers: ljin, rven, yhchiang, igor

Reviewed By: igor

Subscribers: dhruba, MarkCallaghan, leveldb

Differential Revision: https://reviews.facebook.net/D28365
Merge pull request #386 from EugenePig/java8

suppress JDK8 errors for #385
Improve DBTest.GroupCommitTest: artificially slowdown log writing to trigger group commit

Summary: In order to avoid random failure of DBTest.GroupCommitTest, artificially sleep 100 microseconds in each log writing.

Test Plan: Run the test in a machine where valgrind version of the test always fails multiple times and see it always succeed.

Reviewers: igor, yhchiang, rven, ljin

Reviewed By: ljin

Subscribers: leveldb, dhruba

Differential Revision: https://reviews.facebook.net/D28401
update HISOTRY.md for new release

Summary:
as title

Test Plan:
n/a
Turn -Wshadow back on

Summary: It turns out that -Wshadow has different rules for gcc than clang. Previous commit fixed clang. This commits fixes the rest of the warnings for gcc.

Test Plan: compiles

Reviewers: ljin, yhchiang, rven, sdong

Reviewed By: sdong

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D28131