Fix XFIXES selection handling (copy and paste via middle mouse button) (207_nxagent_fix-xfixes-selection.full.patch).

  When nxagent has the XFIXES extension enabled copy and
  paste from outside applications to applications within the session
  that rely on XFixesSelectSelectionInput (e.g. qt applications like
  konsole) did never receive any notifications because the nxagent did
  not register itself at the real X server to receive them. Fixes X2Go Bug
  #585 (http://bugs.x2go.org/585).