File to QString

Read a file and parse whole content to a QString:
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```c
QString fileToString( const QString &fileName, const QString &caller )
{
    QFile file( fileName );

    if( !file.open(QFile::ReadOnly | QFile::Text))
    {
        QMessageBox::warning( 0l, caller, 
                              "Cannot read file "
                              +fileName+":\n"
                              +file.errorString());
        return "";
    }

    QTextStream in( &file );
    QString text = in.readAll();
    file.close();

    return text;
}
```

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