[update 2.0] #20250

20250
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Issue 6503: ScriptLoader deletePackage: does not say what it says
        http://code.google.com/p/pharo/issues/detail?id=6503
       
Issue 6542: unload package Polymorph
        http://code.google.com/p/pharo/issues/detail?id=6542
       
Issue 6544: [ENH]: SystemPreferences - Notify Errors
        http://code.google.com/p/pharo/issues/detail?id=6544
       
Issue 6545: There are no accesses to commandLine in CommandLineHandlerTest
        http://code.google.com/p/pharo/issues/detail?id=6545