load: fix update from differences with zone-in-journal

zone_update_from_differences() invoked in load.c:171 saved some data from journal_contents to the zone contents, which are later freed and this sometimes lead to crashes. The fix introduces a new flag to differentiate whether the zone's own contents or journal's contents are used when invoking zone_update_from_differences() and adjusts its behaviour accordingly. Also a minor leak of glue data caused by an unfortunate memmove() was discovered and fixed.