Merge branch 'jc/am-report-3way'

When "git am -3" needs to fall back to an application to a synthesized preimage followed by a 3-way merge, the paths that needed such treatment are now reported to the end user, so that the result in them can be eyeballed with extra care. * jc/am-report-3way: am -3: list the paths that needed 3-way fallback