(TK-64) Fix TK failures from Slingshot Exceptions

Fix IllegalArgumentException that occurs when catching a
Slingshot exception in the TK main function by adding an
else clause to the case statement.
I tend to agree with @KevinCorcoran that we might be hiding other useful data from the Slingshot exception if we just peel the stack trace off.  For example, I think if you have a cause nested in the exception, re-throwing might allow you to see the stack trace for the cause as well.  I'd be okay re-throwing the exception and am not too concerned about it looking too ugly.