C API: bugfix column_family_comact_range
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slightly reword the sentence to avoid mentioning it.
Merge pull request #199 from jrobeson/patch-1

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Merge pull request #198 from rdallman/cf-compact-range

C API: bugfix column_family_compact_range
C API: update options w/ convenience funcs & fifo compaction
Merge pull request #197 from rdallman/update-options

C API: update options w/ convenience funcs & fifo compaction
Apply fractional cascading in ForwardIterator::Seek()

Summary:
Use search hint to reduce FindFile range thus avoid comparison
For a small DB with 50M keys, perf_context counter shows it reduces
comparison from 2B to 1.3B for a 15-minute run. No perf change was
observed for 1 seek thread, but quite good improvement was seen for 32
seek threads, when CPU was busy.
will post detail results when ready

Test Plan: db_bench and db_test

Reviewers: haobo, sdong, dhruba, igor

Reviewed By: igor

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D18879
generic rate limiter

Summary:
A generic rate limiter that can be shared by threads and rocksdb
instances. Will use this to smooth out write traffic generated by
compaction and flush. This will help us get better p99 behavior on flash
storage.

Test Plan:
unit test output
==== Test RateLimiterTest.Rate
request size [1 - 1023], limit 10 KB/sec, actual rate: 10.374969 KB/sec, elapsed 2002265
request size [1 - 2047], limit 20 KB/sec, actual rate: 20.771242 KB/sec, elapsed 2002139
request size [1 - 4095], limit 40 KB/sec, actual rate: 41.285299 KB/sec, elapsed 2202424
request size [1 - 8191], limit 80 KB/sec, actual rate: 81.371605 KB/sec, elapsed 2402558
request size [1 - 16383], limit 160 KB/sec, actual rate: 162.541268 KB/sec, elapsed 3303500

Reviewers: yhchiang, igor, sdong

Reviewed By: sdong

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19359