MEC import could forget additions to map of source object->target object

Applies to: MetaEdit+ 5.5
Updated package versions: METypeManager::3.9.3

* Fix: Serious error dialog shown when importing MEC file (or MET file with 
  static ports), if an earlier MEC/MET import from the same source repository 
  had been committed, and since then a second MEC/MET from the same source 
  repository had been imported then abandoned in this session, and this third 
  import shared objects with the old
* Fix: Error #at:ifAbsentPut: importing MEC file (or MET file with static 
  ports), if an earlier MEC/MET import from the same source repository had been
  committed, and since then a second MEC/MET from the same source repository 
  but including objects from a new source project had been imported then 
  abandoned in this session, and this third import also contained objects 
  from the new source project.
* Correction: Duplicate objects after importing MEC file (or MET file with 
  static ports), if an earlier MEC/MET import from the same source repository 
  had been committed, and since then a second MEC/MET from the same source 
  repository and source project had been imported then committed, and this 
  third MEC/MET import was in a new session and shared objects with the second.