bug#5649: 23.1.92; Indentation problems in C mode

[Chong Yidong <cyd@stupidchicken.com>]

Michael Welsh Duggan <mwd@cert.org> writes:

> I'm getting some screwy indentation behavior from C mode.  From a
> current bzr checkout/install of emacs, try the following recipe:
>
> emacs -Q foo.c                 | starts emacs on foo.c (included below)
> C-u 7 C-n                      | move down 7 lines
> TAB                            | indent, nothing changes (good)
> C-p C-p                        | move up 2 lines
> TAB C-n TAB C-n                | indent 2 lines, nothing changes (good)
> TAB                            | line unindents by 2 (bad)
> TAB                            | line re-indents (good, but strange)
> TAB                            | no change this time

Thanks.  This is a regression vs Emacs 23.1, so we should definitely fix
it before releasing Emacs 23.2.

I can reproduce the bug with the Emacs 23.0.90, so it's be around since
at lease 12-09 last year.  However, I haven't yet had the time to do a
proper bisect.