Provide instance()-method for Utils::NetworkAccessManager.

Preemptively fix exit warning "QEventLoop cannot be used
without QApplication" (Qt 5/dev) emitted by destruction of
the of the generic highlighter manager singleton which had a
member of type Utils::NetworkAccessManager.

Use a single instance of Utils::NetworkAccessManager for the
main thread and clean up properly using a qAddPostRoutine().

Change-Id: Ida57b9028a79eb4927818ce49088ea567f3bdfd6
Reviewed-by: hjk <hjk121@nokiamail.com>
Reviewed-by: Peter Hartmann <phartmann@blackberry.com>
Reviewed-by: Eike Ziller <eike.ziller@digia.com>

src/libs/utils/networkaccessmanager.cpp

@@ -43,10 +43,30 @@
    \brief Network Access Manager for use with Qt Creator.
 
    Common initialization, Qt Creator User Agent
+
+   Preferably, the instance returned by NetworkAccessManager::instance() should be used for the main
+   thread. The constructor is provided only for multithreaded use.
  */
 
 namespace Utils {
 
+static NetworkAccessManager *namInstance = 0;
+
+void cleanupNetworkAccessManager()
+{
+    delete namInstance;
+    namInstance = 0;
+}
+
+NetworkAccessManager *NetworkAccessManager::instance()
+{
+    if (!namInstance) {
+        namInstance = new NetworkAccessManager;
+        qAddPostRoutine(cleanupNetworkAccessManager);
+    }
+    return namInstance;
+}
+
 static const QString getOsString()
 {
     QString osString;