The patch should be broken into several, one for each bug fix or
enhancement.

Remarks and questions:
- is the readline v6.x fix (which I'm interested in) compatible with
previous readline versions?
- what does "removes '~$-/' from the completer chars list to make the
next item work" mean exactly? is it a bugfix or a new feature?
- I'm not sure filename completion is uncontroversial, it's the kind of
advanced features which we usually let third-party tools (e.g. IPython)
handle if they want to; it may also cause spurious IOs and error messages