desc: 1081 union two streams
tests:

    - rb: r.db('test').table_create('t309')
      def: t = r.db('test').table('t309')

    - rb: t.insert([{'id':0}, {'id':1}])

    - rb: r([]).union([]).typeof
      ot: ("ARRAY")
    - rb: t.union(t).typeof
      ot: ("STREAM")
    - rb: t.union([]).typeof
      ot: ("STREAM")

    - rb: r.db('test').table_drop('t309')

    - rb: r.table_create('1081')
      ot: ({'created':1})

    - rb: r.table('1081').insert({:password => 0})[:inserted]
      ot: 1

    - rb: r.table('1081').index_create('password')
      ot: ({'created':1})

    - rb: r.table('1081').get_all(0, :index => 'password').typeof
      ot: ("SELECTION<STREAM>")
    - rb: r.table('1081').get_all(0, :index => 'password').without('id').typeof
      ot: ("STREAM")
    - rb: r.table('1081').get_all(0, 0, :index => 'password').typeof
      ot: ("SELECTION<STREAM>")
    - rb: r.table('1081').get_all(0, 0, :index => 'password').without('id').typeof
      ot: ("STREAM")

    - rb: r.table_drop('1081')
      ot: ({'dropped':1})
