Plot2d bugs 694770 and 710677



> And plotting implicitly starts from a fixed number of 
> samples, so we could potentially miss poles if the pole is 
> narrow enough and the sampling coarse enough.  Don't think we 
> could ever be smart enough to find a pole like that.

The right way to think of plotting is *not* evaluation at points, but
evaluation on intervals.  With intervals, narrow poles and sin(1/x) and
all that "just work".  But of course we need to implement intervals
first....

      -s