title: How to unwind (multi-level return) the stack without catch/try/raise?
body: <p>I would like to unwind the stack to an arbitrary level when <code>catch</code>/<code>try</code> is not available (i.e., the code to which I'm unwinding is out of my control). Is this possible?</p>
  
  <p>For example, in testing, I would like to have my tests call a method that checks for prerequisites, and unwinds to the caller of the test if those prereqs aren't met (resume at <code>caller[1]</code>).  Since the test harness is out of my control, I can't set up a <code>catch</code> block at the appropriate place.</p>