Add previous breakpoint and function to return previous breakpoint

I needed the ability to know which breakpoint had just been exited, so I made a few updates.  Added a function 'getPrvBreakpoint()' which returns the previous breakpoint or an empty string.  In addition, to make it so you don't need to always call getBreakpoint or getPrvBreakpoint, I added parameters to the .call() requests that pass the "curr" and (the new) "prvBrkpnt" variables as attributes to the Enter/Exit functions.