A partial attempt to improve :stepover

A partial attempt to improve :stepover

  With this patch, :stepover can effectively appear to step over recursive calls and
  calls to locally bound functions (in a where clause).

  However, when we run out of ticks in the current expression,
  the illusion vanishes and laziness brings us to the body of the last function
  we "stepped over".
  This is not desired at all, it is potentially very confusing.
  As a countermeasure, when this happens :stepover emits a warning

     "Warning: no more breakpoints in this function body, switching to :step"