Disable target selection combobox if necessary

 * Set the first target to active in the addtargetdialog's
   target selection combobox
 * Disable the combobox if there is only one element in it.

src/plugins/projectexplorer/addtargetdialog.cpp

@@ -47,6 +47,8 @@ AddTargetDialog::AddTargetDialog(Project *project, QWidget *parent) :
         ui->targetComboBox->addItem(m_project->targetFactory()->displayNameForId(id),
                                     id);
     }
+    ui->targetComboBox->setCurrentIndex(0);
+    ui->targetComboBox->setEnabled(ui->targetComboBox->count() > 1);
 
     connect(ui->buttonBox, SIGNAL(accepted()),
             this, SLOT(accept()));