Added cert filter for SymbianOS

src/plugins/qt4projectmanager/qt-s60/s60createpackagestep.cpp

@@ -645,6 +645,7 @@ S60CreatePackageStepConfigWidget::S60CreatePackageStepConfigWidget(S60CreatePack
 {
     m_ui.setupUi(this);
     m_ui.signaturePath->setExpectedKind(Utils::PathChooser::File);
+    m_ui.signaturePath->setPromptDialogFilter(QLatin1String("*.cer"));
     m_ui.keyFilePath->setExpectedKind(Utils::PathChooser::File);
     updateUi();
     connect(m_ui.customCertificateButton, SIGNAL(clicked()),