Fix bugs introduced by D17961

Summary:
D17961 has two bugs:
(1) two level iterator fails to populate FileMetaData.table_reader, causing performance regression.
(2) table cache handle the !status.ok() case in the wrong place, causing seg fault which shouldn't happen.

Test Plan: make all check

Reviewers: ljin, igor, haobo

Reviewed By: ljin

CC: yhchiang, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D17991
[Java] Add a basic binding and test for BackupableDB and StackableDB.

Summary:
Add a skeleton binding and test for BackupableDB which shows that BackupableDB
and RocksDB can share the same JNI calls.

Test Plan:
make rocksdbjava
make jtest

Reviewers: haobo, ankgup87, sdong, dhruba

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17793