types.h: add missing include

    error: use of overloaded operator '<<' is ambiguous (with operand types 'QDataStream' and 'qint32' (aka 'int'))
    inline QDataStream &operator<<(QDataStream &out, const SignedId &signedId) { out << signedId.toInt(); return out; }
                                                                                 ~~~ ^  ~~~~~~~~~~~~~~~~
    ../../Qt/5.0.2/5.0.2/clang_64/include/QtCore/qchar.h:395:28: note: candidate function
    Q_CORE_EXPORT QDataStream &operator<<(QDataStream &, QChar);
                               ^
    ../../Qt/5.0.2/5.0.2/clang_64/include/QtCore/qvariant.h:527:28: note: candidate function
    Q_CORE_EXPORT QDataStream& operator<< (QDataStream& s, const QVariant& p);
                               ^
    [...]