Align to IEEE 1003.1-2013 + Aardvark 735-737

Regarding issue #17, aligns to IEEE 1003.1-2013 original standard Shell Grammar Rules merging final accepted solutions for issues [735](http://austingroupbugs.net/view.php?id=735), [736](http://austingroupbugs.net/view.php?id=736), and [737](http://austingroupbugs.net/view.php?id=737) in the Austin Group Defect Tracker. The corresponding changes were previously applied to the `parser.y` module during pull-requests #30, #31, #32, and #33. Aligning to the original standard `yacc(1)` source code for Shell and its exact formatting is meant to help tracking the three mentioned Aardvark bugs until closed.