[update 2.0] #20246

20246
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Issue 6518: SystemChangeNotifier - cleanup step 4
        http://code.google.com/p/pharo/issues/detail?id=6518
       
Issue 6524: StartupPreferences loads non-Smalltalk files
        http://code.google.com/p/pharo/issues/detail?id=6524
       
Issue 6528: GroupAnnouncer announcer DNU
        http://code.google.com/p/pharo/issues/detail?id=6528
       
Issue 6529: Method changes not picked up by MC Browser
        http://code.google.com/p/pharo/issues/detail?id=6529