Hmm.  This is looking like a bigger task than I bargained for.  I notice 
that the readline library currently has no tests (or maybe I'm just 
failing to find them).  I'm not even sure how to go about writing tests 
for readline.

> IMHO the patch should try to stay as close to GNU readline's interface 
> as possible, and should therefore fix the off-by-one difference you 
> mention.

I suppose so.  I'm a bit worried about subtle bugs occurring as a result 
of fixing off-by-one differences in some places and missing them in 
others;  it seems safer to provide direct access to the library behaviour 
without trying to fix anything.  Third-party stuff that wants to work with 
Apple's Python is also going to have to deal with zero-based history.  So 
I guess I'd prefer not to fix the off-by-one difference;  this would make 
it even more important to provide some way for users to tell whether 
they're using GNU readline or the wrapped libedit version.

Thanks for the ipython suggestion;  I've never used it before, but I'll 
see if I can play around with it a bit.