code: private Block<Void> toBlock(final Runnable code) {
  		return new Block<Void>() {
  			public Void run() {
  				code.run();
  				return null;
  			}
  		};
  	}
docs: Transforms a Runnable into a Block, so that we need only one
  implementation of the time-traveling code
  
  @param code
  The Runnable to be converted
  @return A Block that, when called, executes the given Runnable