Crash with shell script rule #362

Fixed use-after-release of the "interpreter" variable that was
causing a crash when shell scripts were executed.  The value of
the variable was being retrieved from shebangArgs without being
retained, and then the object was removed from shebangArgs in the
next line, which released the value.
Merge pull request #363 from jhoos/issue_362

Fix for issue #362: Crash with shell script rule. Thank you!