localrepo: prevent executable-bit only changes from being lost on amend If you have just executable-bit change and amend it twice it will vanish: * After the first amend the commit will have the proper executable bit set in manifest but it won't have the the file on the list of files in changelog. * The second amend will read the wrong list of files from changelog and it will copy the manifest entry from parent for this file. * Voila! The change is lost. This change repairs the bug in localrepo causing this and adds a test for it.