Added a compile time define to detect an installer version

QGCInstaller.pri

@@ -18,6 +18,7 @@
 # -------------------------------------------------
 
 installer {
+    DEFINES += __installer_version__
     MacBuild {
         VideoEnabled {
             # Install the gstreamer framework

src/QGCApplication.cc

@@ -134,6 +134,7 @@ static QObject* mavManagerSingletonFactory(QQmlEngine*, QJSEngine*)
 #if defined(QGC_GST_STREAMING)
 #ifdef Q_OS_MAC
 #ifndef __ios__
+#ifdef __installer_version__
 static void qgcputenv(const QString& key, const QString& root, const QString& path)
 {
     QString value = root + path;
@@ -142,6 +143,7 @@ static void qgcputenv(const QString& key, const QString& root, const QString& pa
 #endif
 #endif
 #endif
+#endif
 
 /**
  * @brief Constructor for the main application.
@@ -280,6 +282,7 @@ QGCApplication::QGCApplication(int &argc, char* argv[], bool unitTesting)
 #if defined(QGC_GST_STREAMING)
 #ifdef Q_OS_MAC
 #ifndef __ios__
+#ifdef __installer_version__
     QString currentDir = QCoreApplication::applicationDirPath();
     qgcputenv("GST_PLUGIN_SCANNER",           currentDir, "/gst-plugin-scanner");
     qgcputenv("GTK_PATH",                     currentDir, "/../Frameworks/GStreamer.framework/Versions/Current");
@@ -294,6 +297,7 @@ QGCApplication::QGCApplication(int &argc, char* argv[], bool unitTesting)
 //    }
 #endif
 #endif
+#endif
 #endif
 
     qmlRegisterType<VideoItem>("QGroundControl.QgcQtGStreamer", 1, 0, "VideoItem");