Failing tests

[AtnNn]

After fixing #2 I now see 10 of 2054 tests failed. For example:

Section test_upstream_joins: Tests that manipulation data in tables
  FAILURE in ‘ij.count().run(*conn)’:
    Expected: ‘2500’
     but got: ‘Error("runtime error: No attribute `a` in object:
{
        "b":    3,
        "id":   43
}")’
Section test_upstream_control: Tests RQL control flow structures
  FAILURE in ‘R::expr(5).do_(R::row).run(*conn)’:
    Expected: ‘5’
     but got: ‘null’
Section test_upstream_transform_map: Tests the RQL `map` function
  FAILURE in ‘R::range().map(R::expr(R::array(1, 2, 3, 4)), [=](R::Var x, R::Var y){ return R::array(*x, *y); }).run(*conn)’:
    Expected: ‘[[0,1],[1,2],[2,3],[3,4]]’
     but got: ‘[[1,0],[2,1],[3,2],[4,3]]’

[AtnNn]

After examining the code, I discovered that the handling of variables when converting lambdas to reql seems completely broken.