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/plugins/git/gitorious/gitorious.h

@@ -36,7 +36,6 @@
 #include <QObject>
 
 QT_BEGIN_NAMESPACE
-class QNetworkAccessManager;
 class QNetworkReply;
 class QDebug;
 class QUrl;
@@ -159,7 +158,7 @@ private slots:
     void slotReplyFinished();
 
 private:
-    Gitorious();
+    Gitorious() {}
     void listProjectsReply(int hostIndex, int page, const QByteArray &data);
     void listCategoriesReply(int index, QByteArray data);
     void emitError(const QString &e);
@@ -167,7 +166,6 @@ private:
     void startProjectsRequest(int index, int page = 1);
 
     QList<GitoriousHost> m_hosts;
-    QNetworkAccessManager *m_networkManager;
 };
 
 } // namespace Internal