Move compaction picker and internal key comparator to ColumnFamilyData

Summary: Compaction picker and internal key comparator are different for each column family (not global), so they should live in ColumnFamilyData

Test Plan: make check

Reviewers: dhruba, haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D15801
Fix corruption_test failure caused by auto-enablement of checksum verification.

Summary:
Patch  https://reviews.facebook.net/D15591 enabled checksum
verification by default. This caused the unit test to fail.

Test Plan: ./corruption_test

Reviewers: igor, kailiu

Reviewed By: igor

CC: leveldb

Differential Revision: https://reviews.facebook.net/D15795
Merge branch 'master' into columnfamilies
Fix reduce_levels_test
Compacting column families

Summary: This diff enables non-default column families to get compacted both automatically and also by calling CompactRange()

Test Plan: make check

Reviewers: dhruba, haobo, kailiu, sdong

CC: leveldb

Differential Revision: https://reviews.facebook.net/D15813