Made error messages not use "argument(s)".
Merge branch 'next' into sam_2568

Conflicts:
	test/rql_test/src/arity.yaml
	test/rql_test/src/control.yaml
	test/rql_test/src/meta/table.yaml
	test/rql_test/src/mutation/replace.yaml
	test/rql_test/src/mutation/update.yaml
	test/rql_test/src/selection.yaml
Removed "(s)" pluralization in util.coffee.
Removed "(s)" pluralization in ast.py.
Removed "(s)" pluralization in func.rb.
Removed (s) expectation from rql_test/connections/{cursor.js,promise.js}.
Fixed missing syntax in cursor.js.
Fixed direction of "plural" function in util.coffee.  (Sigh.)
Merge branch 'sam_2568' into next
Merge branch 'next' into sam_2156_env_4