Revision 1382

* fixed a crash when selecting 'New' or opening another file while being
  attached to the sampler
* don't allow the user to remove an instrument while being attached to the
  sampler, because it wouldn't end well ;-)
* don't show a 'file modified' confirmation dialog when closing/quitting
  the application and being attached to the sampler, since the
  modifications won't be lost until the sampler was quit
* while beng attached to the sampler, show the user an information dialog
  when he selects 'New' or 'Open', since this will detach gigedit from the
  sampler
* updated German translation