Fixed unbound vars and implemented some bash good practices#27

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na-- wants to merge 3 commits intocescoffier:masterfrom na--:master

+7-5

Commits on Dec 9, 2014

Implemented some bash good practices for failing early when there is an error ( http://kvz.io/blog/2013/11/21/bash-best-practices/ )
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Fixed a few unbound variables
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Fixed error reporting for invalid options
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