Sent upstream: https://github.com/aarnt/octopkg/pull/4

commit 5f02bb3e504d1d3560ee5a7a3d7c0f90b25adac5
Author: Raphael Kubo da Costa <rakuco@FreeBSD.org>
Date:   Thu Jan 21 13:27:57 2016 +0100

    QtSolutions: Fix build with Qt 5.5.1.

    Import commit ad9bc4600 to the qt-solutions git repository:
      QtSingleApplication: Fix build with Qt 5.5 due to the QDataStream
      include cleanup.

    This fixes the following error:

    src/QtSolutions/qtlocalpeer.cpp:159:17: error: variable has incomplete type 'QDataStream'
        QDataStream ds(&socket);
                    ^
    /usr/local/include/qt5/QtCore/qglobal.h:570:7: note: forward declaration of 'QDataStream'
    class QDataStream;
          ^
    src/QtSolutions/qtlocalpeer.cpp:179:17: error: variable has incomplete type 'QDataStream'
        QDataStream ds(socket);
                    ^
    /usr/local/include/qt5/QtCore/qglobal.h:570:7: note: forward declaration of 'QDataStream'
    class QDataStream;
          ^

--- src/QtSolutions/qtlocalpeer.cpp
+++ src/QtSolutions/qtlocalpeer.cpp
@@ -40,6 +40,7 @@
 
 #include "qtlocalpeer.h"
 #include <QtCore/QCoreApplication>
+#include <QtCore/QDataStream>
 #include <QtCore/QTime>
 #include <QRegularExpression>