bugfixen in source breakpoints and in-procedure traps

bugfixen in source breakpoints and in-procedure traps

* module/system/vm/traps.scm (trap-in-procedure): If we are
  (re-)entering the procedure from a return, call the enter-proc with
  the returnee, not the returner.
  (in-range?): Tighten up a bit.
  (program-sources-before-retire): New helper, like program-sources but
  indexed before instructions are retired instead of after.
  (program-sources-by-line): Use program-sources-before-retire so that
  we can break on instructions by source line *before* those
  instructions are executed.