"git am" and then "git am -3" regression?

[Junio C Hamano <gitster@pobox.com>]

Hmm, there seems to be some glitches around running "am -3"
after a failed "am" between 'maint' and 'master'.

When I try the following sequence, the 'am' from 'maint' succeeds,
but 'am' in 'master' fails:

 * Save Eric's "minor documetation improvements" $gmane/274537
   to a file.  

 * "git checkout e177995" (that's "next^0") and then apply them with
   "git am" (no -3 necessary).

 * "git checkout 272be14" (that's "es/worktree-add-cleanup^0") and
   then apply them with "git am" (without -3).

   This is expected to stop at 2/6, as the context has changed
   between 272be14 and the tip of 'next'.

 * "git am -3".  This should restart and resolve cleanly.

Reverting d96a275b91bae1800cd43be0651e886e7e042a17 seems to fix it,
so that is what I'll do for 2.5 final.

I think Paul's builtin-am has the same issues, that would need a
separate fix.

commit d96a275b91bae1800cd43be0651e886e7e042a17
Author: Remi Lespinet <remi.lespinet@ensimag.grenoble-inp.fr>
Date:   Thu Jun 4 17:04:55 2015 +0200

    git-am: add am.threeWay config variable
    
    Add the am.threeWay configuration variable to use the -3 or --3way
    option of git am by default. When am.threeway is set and not desired
    for a specific git am command, the --no-3way option can be used to
    override it.