Sloved a serious problem in heavily client login-logoff. add a rubbish can, hold sockets to be deleted later

a bug caused by m_currentBlock.constData() has been fixed. the pointer returned by this method will be unavaliable when the block has been changed.

const QByteArray & type paras, will cause lift cycle problems. using Value-pass instead.
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QString, QByteArray supports ref-count and auto-delete , also, these classes support
least-copying, deep-copy will only take place, when the data is about to be changed.
so, in singnals and slots, using QString, QByteArray instead of const QString & and const QByteArray & ,
will not cause performance problem.

Each server instance knows exactly how many clients each server currently have.

It is very strange, that in GNU C++ in Ubuntu, inline-member funcs called by different thread will return zero values.