Avoid reloading filter on Get() if cache_index_and_filter_blocks == false

Summary:
This fixes the case that filter policy is missing in SST file, but we
open the table with filter policy on and cache_index_and_filter_blocks =
false. The current behavior is that we will try to load it every time on
Get() but fail.

Test Plan: unit test

Reviewers: yhchiang, igor, rven, sdong

Reviewed By: sdong

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D25455
fix table_test

Summary:
SaveValue expects an internal key but I previously added to table a
user key

Test Plan:
ran the test
Printing number of keys in DB Stats

Summary: It is useful to print out number of keys in DB Stats

Test Plan:
./db_bench --benchmarks fillrandom --num 1000000 -threads 16 -batch_size=16

and watch the outputs in LOG files

Reviewers: MarkCallaghan, ljin, yhchiang, igor

Reviewed By: igor

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D24513
db_bench: --batch_size used for write benchmarks too

Summary: Now --bench_size is only used in multireadrandom tests, although the codes allow it to run in all write tests. I don't see a reason why we can't enable it.

Test Plan:
Run
   ./db_bench -benchmarks multirandomwrite --threads=5 -batch_size=16
and see the stats printed out in LOG to make sure batching really happened.

Reviewers: ljin, yhchiang, rven, igor

Reviewed By: igor

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D25509