Iterator support for Write Batches
Test for WriteBatchHandler
Addresed comments from code review https://reviews.facebook.net/D27567
Make ForwardIterator::status() more efficient

Summary:
In D19581 I made `ForwardIterator::status()` check all child iterators,
including immutable ones. It's, however, not necessary to do it every
time -- it'll suffice to check only when they're used and their status
could change.

This diff:
* introduces `immutable_status_` which is updated by `Seek()` and `Next()`
* removes special handling of `kIncomplete` status in those methods

Test Plan:
* `db_test`
* hacked ReadSequential in db_bench.cc to check `status()` in addition to
  validity:

```
   $ ./db_bench -use_existing_db -benchmarks readseq -disable_auto_compactions \
      -use_tailing_iterator  # without this patch
   Keys:       16 bytes each
   Values:     100 bytes each (50 bytes after compression)
   Entries:    1000000
   [...]
   DB path: [/dev/shm/rocksdbtest/dbbench]
   readseq      :       0.562 micros/op 1778103 ops/sec;   98.4 MB/s
   $ ./db_bench -use_existing_db -benchmarks readseq -disable_auto_compactions \
      -use_tailing_iterator  # with the patch
   readseq      :       0.433 micros/op 2311363 ops/sec;  127.8 MB/s
```

Reviewers: igor, sdong, ljin

Reviewed By: ljin

Subscribers: dhruba, leveldb, march, lovro

Differential Revision: https://reviews.facebook.net/D24063
Merge pull request #363 from adamretter/write_batch-iterate

Iterator support for Write Batches
[RocksJava] Makefile restructured
[RocksJava] Flush functionality

RocksJava now supports also flush functionality of
RocksDB.
Merge pull request #393 from fyrz/RocksJava-Flush

[RocksJava] Memtable flush functionality
Fix NewFileNumber()

Summary: I mistakenly changed the behavior to ++next_file_number_ instead of next_file_number_++, as it should have been: https://github.com/facebook/rocksdb/blob/344edbb044ff5c08a43e4a6e9344c5c861552c0e/db/version_set.h#L539

Test Plan: none. not sure if this would break anything. It's just different behavior, so I'd rather not risk

Reviewers: ljin, rven, yhchiang, sdong

Reviewed By: sdong

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D28557