thread local for tailing iterator

Summary:
replace the super version acquisision in tailing itrator with thread
local

Test Plan: will post results

Reviewers: igor, haobo, sdong, yhchiang, dhruba

Reviewed By: igor

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17757
Fix merge_test failure due to incorrect assert behavior in the release mode.
Expose in memory Env to the world

Summary: That will help with some iOS testing I'm doing.

Test Plan: compiles

Reviewers: dhruba, haobo, ljin, yhchiang, sdong

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17787
[JNI] Each set function of Options / WriteOptions now returns its option instance.

Summary:
Make each set function of Options / WriteOptions return its option instance.
Java developers can now easier specify each option like the following:

    options.setCreateIfMissing(true)
        .setWriteBufferSize(8 * 1024)
        .setMaxWriteBufferNumber(3)
        .setDisableSeekCompaction(true)
        .setBlockSize(64 * 1024)
        .setMaxBackgroundCompactions(10);

Test Plan:
make rocksdbjava
make jtest

Reviewers: haobo, ankgup87, sdong, dhruba

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17661
[JAVA] Add java binding for Options.block_cache.

Summary:
Add java bindings for Options.block_cache and allow DbBenchmark to
set cache_size.

Test Plan:
make rocksdbjava
make jtest
make jdb_Bench

Reviewers: haobo, sdong, ankgup87

Reviewed By: ankgup87

CC: leveldb, dhruba

Differential Revision: https://reviews.facebook.net/D17481
[Java] Add SizeUnit in org.rocksdb.util to store const like KB, GB.

Summary:
* Add a class SizeUnit to store frequently used consts.  Currently
  it has KB, MB, GB, TB, and PB.

* Change the parameter type of Options.writeBufferSize and Options.blockSize
  from int to long.

Test Plan:
make rocksdbjava
make jtest

Reviewers: haobo, ankgup87, sdong, dhruba

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17703
Fix compile error in tailing_iter.h

Summary:
Fix the following compile error

  ./db/tailing_iter.h:17:1: error: class 'SuperVersion' was previously declared as a struct [-Werror,-Wmismatched-tags]
  class SuperVersion;
  ^
  ./db/column_family.h:77:8: note: previous use is here
  struct SuperVersion {
         ^
         ./db/tailing_iter.h:17:1: note: did you mean struct here?
         class SuperVersion;
         ^~~~~
         struct
         1 error generated.

Test Plan: make

Reviewers: ljin, igor, haobo, sdong

Reviewed By: ljin

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17799
Fix db_bench's multireadrandom

Summary: multireadrandom is broken. Fix it

Test Plan: run it and see segfault has gone.

Reviewers: ljin

Reviewed By: ljin

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17781