Long overdue changes and refactoring for qemu handling.

Fixes: - react on build/ run configuration changes
       - now notices environment changes, like switching Qt versions
       - start button is now only shown if we have a valid qemu runtime
       - enabled/ disabled state works properly when loading a project

Task-number: QTCREATOR-210, QTCREATORBUG-1252, QTCREATORBUG-1082
Reviewed-by: ck

src/plugins/qt4projectmanager/qt4projectmanagerplugin.cpp

@@ -153,7 +153,7 @@ bool Qt4ProjectManagerPlugin::initialize(const QStringList &arguments, QString *
     addAutoReleasedObject(new LinguistExternalEditor);
 
     addAutoReleasedObject(new S60Manager);
-    addAutoReleasedObject(new MaemoManager);
+    addAutoReleasedObject(m_maemoManager = new MaemoManager);
 
     new ProFileCacheManager(this);
 
@@ -228,6 +228,7 @@ bool Qt4ProjectManagerPlugin::initialize(const QStringList &arguments, QString *
 void Qt4ProjectManagerPlugin::extensionsInitialized()
 {
     m_qt4ProjectManager->init();
+    m_maemoManager->init(); // depends on the Qt4ProjectManager
 }
 
 void Qt4ProjectManagerPlugin::updateContextMenu(Project *project,