[RFA] fix annoying completion bug on directories

[Daniel Jacobowitz]

FYI, I worked on this once:

  http://sourceware.org/ml/gdb/2004-01/msg00222.html

The result was rl_completion_word_break_hook, which is exactly what
you're using here.  But I never got back to working on it, so we never
took advantage of the new hook even though we imported a new enough
readline.

Thanks for doing this!

Sorry, this is very complicated code; I will have to find another
time to review it.  But I wanted to thank you for fixing the bug.

-- 
Daniel Jacobowitz
CodeSourcery