KProtocolManager extensions for application-specific user agent string

• only adds 'X11' bit for 'p' key in "static QString KProtocolManager::defaultUserAgent(const QString &keys)" for X11-based targets

• adds static QString userAgentForApplication( const QString &appName, const QString& appVersion, const QStringList& extraInfo = QStringList() ); for the application's user-agent string other than web browser (think of KMail/KNode/Mailody..)

• adds static bool getSystemNameVersionAndMachine( QString& systemName, QString& systemVersion, QString& machine ); (returns nicely splitted system name, version and machine type, for example "Windows", "5.1", "i686"; also more useful for various sysinfo reporting)

The example result of userAgentForApplication()
in KMail is then a user agent string like
KMail/1.9.50 (Windows/5.0; KDE/3.97.1; i686; svn-762186; 2008-01-15)

svn path=/trunk/KDE/kdelibs/; revision=771642