use restart text and icon in unsaved changes dialog

[Klumbumbus]

What steps will reproduce the problem?

1. have an unsaved data layer
2. trigger josm restart (by file menu or plugin installation or preference change or...)
3. unsaved changes dialog appears

I always think "why only exit? I wanted to restart!"

If JOSM is about to restart the two left buttons in the unsaved changes dialog should display "restart" instead of "exit" together with the restart icon.

URL:http://josm.openstreetmap.de/svn/trunk
Repository:UUID: 0c6e7542-c601-0410-84e7-c038aed88b3b
Last:Changed Date: 2016-08-10 23:42:43 +0200 (Wed, 10 Aug 2016)
Build-Date:2016-08-11 01:35:54
Revision:10779
Relative:URL: ^/trunk

Identification: JOSM/1.5 (10779 en) Windows 7 32-Bit
Memory Usage: 339 MB / 742 MB (164 MB allocated, but free)
Java version: 1.8.0_101-b13, Oracle Corporation, Java HotSpot(TM) Client VM
VM arguments: [-Djava.security.manager, -Djava.security.policy=file:<java.home>\lib\security\javaws.policy, -DtrustProxy=true, -Djnlpx.home=<java.home>\bin, -Djnlpx.origFilenameArg=C:\Program Files\josm-latest-bla.jnlp, -Djnlpx.remove=false, -Djava.util.Arrays.useLegacyMergeSort=true, -Djnlpx.heapsize=256m,768m, -Djnlpx.splashport=49898, -Djnlpx.jvm=<java.home>\bin\javaw.exe, -Djnlpx.vmargs=LURqYXZhLnV0aWwuQXJyYXlzLnVzZUxlZ2FjeU1lcmdlU29ydD10cnVlAA==]
Dataset consistency test: No problems found