Include command stack actions in saved sessions

[mkoniecz]

What steps will reproduce the problem?

1. Load some OSM data
2. enable command stack menu
3. make edits visible in command stack
4. close JOSM without uploading and use option to save session to joz file
5. open JOSM
6. load saved session from joz file
7. note that command stack is empty and is not displaying not uploaded changes before saving session

What is the expected result?

Command stack is displaying also actions before saving to file

What happens instead?

Command stack is empty and is not displaying not uploaded changes before saving session

Please provide any additional information below. Attach a screenshot if possible.

URL:http://josm.openstreetmap.de/svn/trunk
Repository:UUID: 0c6e7542-c601-0410-84e7-c038aed88b3b
Last:Changed Date: 2016-04-03 19:25:25 +0200 (Sun, 03 Apr 2016)
Build-Date:2016-04-04 01:32:50
Revision:10108
Relative:URL: ^/trunk

Identification: JOSM/1.5 (10108 en) Linux Ubuntu 14.04.4 LTS
Memory Usage: 388 MB / 889 MB (154 MB allocated, but free)
Java version: 1.8.0_77-b03, Oracle Corporation, Java HotSpot(TM) Server VM
Dataset consistency test: No problems found

Plugins:
- OpeningHoursEditor (31772)
- RoadSigns (31895)
- measurement (31895)

Validator rules:
- /home/mateusz/Documents/OSM/josm.validator.mapcss

[Don-vip]

In 14281/josm:

see #12726 - accessors for undo/redo commands

[Don-vip]

In 14283/josm:

see #12726 - add new getters in {Change,Sequence}Command

[Don-vip]

It's major work and will take some time. I've written some stuff which requires stability of primitive IDs first (#16854).

[Don-vip]

In 14348/josm:

see #12726 - new XML util to get first child Element