Conflict dialog: JOSM still uploads data even though there's no need to after a conflict resolution

[avar]

1. Edit way Foo in JOSM, set it to highway=motorway
2. Edit way Foo in Potlatch, set it to highway=residential
3. Edit way Foo in JOSM, set it to highway=unclassified

Now when I try to upload JOSM throws a conflict because I'm trying to upload a highway=unclassified way to the server that has changed to highway=residential since I last saw it, so far so good.

But with the conflict resolved JOSM still thinks the way is modified and will happily upload it to the server even though that will change no data, here's an example of JOSM uploading a changeset (2393) that did nothing:

<?xml version="1.0" encoding="UTF-8"?>
<osm version="0.6" generator="OpenStreetMap server">
  <way id="49792" visible="true" timestamp="2009-12-12T10:54:39Z" user="Ævar Arnfjörð Bjarmason" uid="11" version="1" changeset="2391">
    <nd ref="1168763"/>
    <nd ref="1168764"/>
    <nd ref="1168762"/>
    <nd ref="1168761"/>
    <nd ref="1168763"/>
    <tag k="highway" v="motorway"/>
    <tag k="name" v="bleh"/>
  </way>
  <way id="49792" visible="true" timestamp="2009-12-12T10:55:25Z" user="Ævar Arnfjörð Bjarmason" uid="11" version="2" changeset="2392">
    <nd ref="1168763"/>
    <nd ref="1168764"/>
    <nd ref="1168762"/>
    <nd ref="1168761"/>
    <nd ref="1168763"/>
    <tag k="highway" v="residential"/>
    <tag k="name" v="bleh"/>
  </way>
  <way id="49792" visible="true" timestamp="2009-12-12T10:57:55Z" user="Ævar Arnfjörð Bjarmason" uid="11" version="3" changeset="2393">
    <nd ref="1168763"/>
    <nd ref="1168764"/>
    <nd ref="1168762"/>
    <nd ref="1168761"/>
    <nd ref="1168763"/>
    <tag k="highway" v="residential"/>
    <tag k="name" v="bleh"/>
  </way>
</osm>

Instead JOSM should track the result of conflict resolutions and check if the user opted to keep the server data, if that's the case then it shouldn't needlessly upload it again.

[stoecker]

Related to #4088.

[mjulius]

(In [2624]) fixes #4088,#4155 - when after conflict resolving the primitive has equal semantic attributes as theirs, the primitive will get the same modified flag as theirs.