Add separate Read/WriteUnlock methods in MutexRW.

Some platforms, particularly Windows, do not have a single method that can
release both a held reader lock and a held writer lock; instead, a
separate method (ReleaseSRWLockShared or ReleaseSRWLockExclusive) must be
called in each case.

This may also be necessary to back MutexRW with a shared_mutex in C++14;
the current language proposal includes both an unlock() and a
shared_unlock() method.
Refactor: group metadata needed to open an SST file to a separate copyable struct

Summary:
We added multiple fields to FileMetaData recently and are planning to add more.
This refactoring separate the minimum information for accessing the file. This object is copyable (FileMetaData is not copyable since the ref counter). I hope this refactoring can enable further improvements:

(1) use it to design a more efficient data structure to speed up read queries.
(2) in the future, when we add information of storage level, we can easily do the encoding, instead of enlarge this structure, which might expand memory work set for file meta data.

The definition is same as current EncodedFileMetaData used in two level iterator, so now the logic in two level iterator is easier to understand.

Test Plan: make all check

Reviewers: haobo, igor, ljin

Reviewed By: ljin

Subscribers: leveldb, dhruba, yhchiang

Differential Revision: https://reviews.facebook.net/D18933
Include max_write_buffer_number >= 2 to SanitizeOptions.

Summary: Include max_write_buffer_number >= 2 to SanitizeOptions.

Test Plan: make all check

Reviewers: haobo, sdong, igor, ljin

Reviewed By: ljin

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19077
Merge pull request #176 from bgrainger/mutexrw-unlock

Add separate Read/WriteUnlock methods in MutexRW.
Add a table factory that can read DB with both of PlainTable and BlockBasedTable in it

Summary: The new table factory is used if users want to convert a DB from one table format to the other. A user can use this table to open a DB written using one table format and write new files to another table format.

Test Plan: add a unit test

Reviewers: haobo, igor

Reviewed By: igor

Subscribers: dhruba, ljin, yhchiang, leveldb

Differential Revision: https://reviews.facebook.net/D19017
specify the command to install build_tools/mac-install-gflags.sh file in doc
Merge pull request #177 from nanwu/master

specify the command to install build_tools/mac-install-gflags.sh file in...
HashLinkList to log distribution of number of entries aross buckets

Summary: Add two parameters of hash linked list to log distribution of number of entries across all buckets, and a sample row when there are too many entries in one single bucket.

Test Plan: Turn it on in plain_table_db_test and see the logs.

Reviewers: haobo, ljin

Reviewed By: ljin

Subscribers: leveldb, nkg-, dhruba, yhchiang

Differential Revision: https://reviews.facebook.net/D19095
Change order of parameters in adaptive table factory

Summary:
This is minor, but if we put the writing talbe factory as the third parameter, when we add a new table format, we'll have a situation:
1) block based factory
2) plain table factory
3) output factory
4) new format factory

I think it makes more sense to have output as the first parameter.

Also, fixed a NewAdaptiveTableFactory() call in unit test

Test Plan: unit test

Reviewers: sdong

Reviewed By: sdong

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19119