[RFC] add regenerate Makefile target

[Tom Tromey]

> not sure if the current autoregen.py is in sync with that?

I'm curious why "autoreconf -f" is insufficient.
It seems to me that this should work.

> Also... I discovered the existence of an automake rule:
> am--refresh which IIUC is intended to automake the update of Makefile
> and its dependencies.

Don't use that rule directly.  It's an implementation detail and
shouldn't be relied on.

thanks,
Tom