bug#25105: bug#25400: M-p in diff-mode jumps too far

[Mark Oteiza <mvoteiza@udel.edu>]

On 11/01/17 at 01:38pm, Tino Calancha wrote:
> Stefan Monnier <monnier@IRO.UMontreal.CA> writes:
> 
> > In a buffer with more than one hunk, if I'm in the middle of hunk number
> > N, diff-hunk-prev (usually bound to M-p) jumps to the header of hunk
> > number N-1 rather than to the header of hunk N.
> >
> > This is contrary to the usual behavior of Emacs's navigation commands.
> >As pointed out elsewhere, it's particularly obnoxious from EOB (in which
> >case, you're not really "within N" but you're virtually on "the header
> >of the non-existent hunk N+1", so going to the header of N-1 is really
> >wrong).
> >
> >I also dislike the fact that M-n doesn't let me get to EOB.
> 
> Following patch reverts commit 2c8a7e5.  Then it fixes dots 1. and 2.
> described in the commit message of 2c8a7e5, i.e., Bug#17544.
> This patch preserves the original definitions for 'diff-hunk-prev'
> and 'diff-hunk-next'.
> 
> After applying locally this patch, you might want to do:
> git diff 2c8a7e5^ HEAD lisp/vc/diff-mode.el
> to see more clearly how it solves Bug#17544.

Works for me AFAICT.  Thanks for working on it.