Turn on -Wshorten-64-to-32 and fix all the errors

Summary:
We need to turn on -Wshorten-64-to-32 for mobile. See D1671432 (internal phabricator) for details.

This diff turns on the warning flag and fixes all the errors. There were also some interesting errors that I might call bugs, especially in plain table. Going forward, I think it makes sense to have this flag turned on and be very very careful when converting 64-bit to 32-bit variables.

Test Plan: compiles

Reviewers: ljin, rven, yhchiang, sdong

Reviewed By: yhchiang

Subscribers: bobbaldwin, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D28689
Fix additional -Wshorten-64-to-32 errros
Fixed GetEstimatedActiveKeys

Summary:
Fixed a bug in GetEstimatedActiveKeys which does not normalized
the sampled information correctly.

Add a test in version_builder_test.

Test Plan: version_builder_test

Reviewers: ljin, igor, sdong

Reviewed By: sdong

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D28707
Fixed clang compile error in version_builder_test

Summary: Fixed clang compile error in version_builder_test

Test Plan: ./version_builder_test

Reviewers: igor, sdong

Reviewed By: sdong

Subscribers: sdong, dhruba

Differential Revision: https://reviews.facebook.net/D28731
[RocksJava] Extend Options with ColumnFamilyOptions implementation ColumnFamilyOptions implementation with tests
[RocksJava] Extended ColumnFamilyTest

Summary: Options Refactoring split part 3

Test Plan:
make rocksdbjava
make jtest

Reviewers: yhchiang, ankgup87

Subscribers: dhruba

Differential Revision: https://reviews.facebook.net/D28023
[RocksJava] ColumnFamily custom Options API extension

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[RocksJava] Integrated Review comments from yhchiang in D28023
[RocksJava] Incorporated review comments
[RocksJava] Sample and Default value

- RocksDB ColumnFamilySample adjusted to C++ sample.
- DefaultColumnFamily is available now as constant in RocksDB.
[RocksJava] Code-cleanup + Java7 warnings removed
[RocksJava] JavaDoc cleanup warnings with Java8

Java8 is more restrictive than Java7 with generating
JavaDocs. This commit resolves current existing Java8
warnings.