Debugging information.
Made rdb_batched_replace use a coro pool.
Reverted debugfs.
Fixed include order.
Named a constant in btree.cc.
Reordered destructors in rdb_batched_replace.
Better terminal interface in test/run

Review 1552 by @larkost
Merge branch 'mlucy_changefeed_fixes' into next
Merge branch 'next' of github.com:rethinkdb/rethinkdb into next
Merge branch 'next' into sam_1907