Enable no-fbcode RocksDB build

Summary: I want to use open source build rather than fbcode one. This enables me to run `ROCKSDB_NO_FBCODE=1 make` and run it with my system g++.

Test Plan:
ROCKSDB_NO_FBCODE=1 make
make

Reviewers: sdong, ljin, yhchiang

Reviewed By: yhchiang

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D23613
Skip AllocateTest if fallocate() is not supported in the file system

Summary: To avoid false positive test failures when the file system doesn't support fallocate. In EnvTest.AllocateTest, we first make a simple fallocate call and check the error codes to rule out the possibility that it is not supported. Skip the test if the error code indicates it is not supported.

Test Plan: Run the test and make sure it passes on file systems supporting and not supporting fallocate

Reviewers: yhchiang, ljin, igor

Reviewed By: igor

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D23667
Print compression_size_percent as a signed int

Summary:
compression_size_percent is an int but was printed as
an unsigned int. So the default of -1 is displayed as a big number.

Test Plan: make check

Reviewers: sdong

Reviewed By: sdong

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D23679
Add rate limiter
Merge branch 'master' of https://github.com/facebook/rocksdb