In nxagent sessions, all X11 clients have a representation of their NX
 session-side window object on the real X-Server side.

 The window object gets stored in the new NX_REAL_WINDOW window property
 immediately after window creation. This mapping is created in
 nxagentCreateWindow().

 On session resumption, the client side window IDs normally change. Thus,
 during session resumption, all NX_REAL_WINDOW properties require being
 updated. This happens in nxagentReconnectWindow().

 While a session is suspended, the NX_REAL_WINDOW property does not
 exist. It gets removed during nxagentDisconnectWindow().