Bug in computeTopLevelExpressions for o.p += ...

[esbena]

It seems that that astUtil.computeTopLevelExpressions has a bug.
The following test fails if it is added to topLevelExprTests.js:

it('should handle property increment', function() {
    checkCode("var o = {p: 42}; o.p += 37;",  [25, 49]); // yields [25, 49, 41]
});

Clearly there should only be two top level expressions in that code.

The instrumented code that astUtil.computeTopLevelExpressions operates on is this:

var o = J$.W(25, 'o', J$.T(17, { p: J$.T(9, 42, 22, false) }, 11, false), o, false, true);
J$.A(49, J$.R(33, 'o', o, false, true), 'p', '+')(J$.T(41, 37, 22, false));

Reporting 41 as a top level expression happens because the implementation of astUtil.computeTopLevelExpressions assigns a nesting depth of zero to J$.T(41, …) because it does not recognize the nestedness of J$.A(…)(J$.T(41, …)), an additional case is needed for that pattern.

(I do have a simple fix, I will do a pull request later)