SpatialDB change API

Summary: I changed SpatialDB API so that we only specify list of indexes when we create the database. That way, whoever is querying the DB doesn't need to know the full list of indexes and their options.

Test Plan: spatial_db_test

Reviewers: yinwang

Reviewed By: yinwang

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D20571
Fix compile warning
Fixed compaction-related errors where number of input levels are hard-coded.

Summary:
Fixed compaction-related errors where number of input levels are hard-coded.
It's a bug found in compaction branch.
This diff will be pushed into master.

Test Plan:
export ROCKSDB_TESTS=Compact
make db_test -j32
./db_test
also passed the tests in compaction branch

Reviewers: igor, sdong, ljin

Reviewed By: ljin

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D20577
Fix valgrind test