GH-6: fix gotcha in shell short-circuit evaluation
GH-6: fix gotcha in shell short-circuit evaluation

The POSIX shell language manual describes short-circuit evaluation thus:

    The operators "&&" and "||" shall have equal precedence and shall be
    evaluated with left associativity. For example, both of the
    following commands write solely bar to standard output:

    false && echo foo || echo bar
    true || echo foo && echo bar

http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_09_03

sunaku/dasht