CoffeeScript compatibility issue: do expressions

[bbrk24]

This is a bit of an edge case, but given the following CoffeeScript code:

f = ->
  foo.bar = do
    bar = getBar()
    bar.baz = 3
    bar

CoffeeScript itself produces this:

f = function() {
  var bar;
  foo.bar = (bar = getBar())();
  bar.baz = 3;
  return bar;
};

The indentation is misleading: the lines bar.baz = 3 and bar are not part of the do expression, but statements at the top level of f. Civet with 'civet coffeeCompat' follows the indentation and produces this output:

f = function () {
  var bar;
  return (foo.bar = (bar = getBar()(
    (bar.baz = 3),
    bar
  ))());
};

[edemaine]

Related CoffeeScript issue: jashkenas/coffeescript#5458

Like that proposal, I think Civet should fail to parse / emit an error here (in coffeeCompat mode).