- Avoid sending twice the same status.
- Discard SCARD_E_UNKNOWN_READER error as it's happening when the reader is
disconnected and the disconnection will be detected by the pcsclite.cpp
status thread.
- Allow up to 4 the number of times SCardCancel is called before waiting for
the status `thread` to finish.
- Destroy the mutexes and conds only in the destructors.
- Check that the thread handles are still valid before calling join on them.
Santiago Gimeno