SpatialDB

Summary:
This diff is adding spatial index support to RocksDB.

When creating the DB user specifies a list of spatial indexes. Spatial indexes can cover different areas and have different resolution (i.e. number of tiles). This is useful for supporting different zoom levels.

Each element inserted into SpatialDB has:
* a bounding box, which determines how will the element be indexed
* string blob, which will usually be WKB representation of the polygon (http://en.wikipedia.org/wiki/Well-known_text)
* feature set, which is a map of key-value pairs, where value can be int, double, bool, null or a string. FeatureSet will be a set of tags associated with geo elements (for example, 'road': 'highway' and similar)
* a list of indexes to insert the element in. For example, small river element will be inserted in index for high zoom level, while country border will be inserted in all indexes (including the index for low zoom level).

Each query is executed on single spatial index. Query guarantees that it will return all elements intersecting the specified bounding box, but it might also return some extra non-intersecting elements.

Test Plan: Added bunch of unit tests in spatial_db_test

Reviewers: dhruba, yinwang

Reviewed By: yinwang

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D20361
Use IterKey instead of string in Block::Iter to reduce malloc

Summary:
  Modify a functioin TrimAppend in dbformat.h: IterKey. Write a test for it in dbformat_test
  Use IterKey in block::Iter to replace std::string to reduce malloc.

  Evaluate it using perf record.
  malloc: 4.26% -> 2.91%
  free: 3.61% -> 3.08%

Test Plan:
  make all check
  ./valgrind db_test dbformat_test

Reviewers: ljin, haobo, yhchiang, dhruba, igor, sdong

Reviewed By: sdong

Differential Revision: https://reviews.facebook.net/D20433
Fix release compile error
NewIterators in read-only mode

Summary: As title.

Test Plan: Added test to column_family_test

Reviewers: ljin, yhchiang, sdong

Reviewed By: sdong

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D20523
[Java] Add compaction style to options

Summary:
Add compression type to options

make rocksdbjava
make sample

Reviewers: haobo, yhchiang, sdong, dhruba, rsumbaly, zzbennett, swapnilghike
Reviewed By: yhchiang, sdong
CC: leveldb

Differential Revision: https://reviews.facebook.net/D20463
Merge branch 'ankgup87-master'