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
Made db_term_t use the cluster_access.databases_semilattice_metadata watchable.
Replaced other thread-crossing use of db_searcher, removed db_searcher from const_rethreading_metadata_accessor_t.
Removed unnecessarily cross-threaded const_rethreading_metadata_accessor_t::ns_searcher uses.
Removed comment about semilattice_metadata.
Merge branch 'next' into sam_1907
Merge branch 'sam_1907' into next
Merge branch 'next' into sam_2156

Conflicts:
	src/rdb_protocol/env.hpp