Fix order_by on empty sequences.
Fix argument check in order_by.
Fix code style.
Draft release notes for 1.12.5
Merge pull request #2423 from rethinkdb/atnnn/notes

Draft release notes for 1.12.5
Fix for #2425, CR 1526
Merge branch 'v1.12.x' into next

Conflicts:
	src/rdb_protocol/env.cc
Merge branch 'next' into sam_2156