BRANCH 4.2-106:
  made the use_transaction of API call execute_cmd actually work by introducing a TRANS_OPTIONAL_METHODS dict.
  made the ThumbCmd run without recording transaction
  made the process_video function in IconCreator produce a proper icon_path using subprocess.call()
BRANCH 4.2-106:
  made the left right and Enter Esc key work in the GalleryWdg at all times