inheritance fix

[Tim Schaub]

When support for @extends was added [1], I didn't properly handle
augmentation from more than first level parents.

I've issued a pull request [2] that brings support for arbitrarily
deep lines of inheritance. The new tests demonstrate what doesn't
work currently.

Thanks for any comments/review.

Tim

[1] https://github.com/micmath/jsdoc/pull/35
[2] https://github.com/micmath/jsdoc/pull/83