Close all frame grabbers.
The operator ::close_all_framegrabbers closes all frame grabbers. It is used to cope with deadlocks resulting from damaged frame grabber handles (in that case the use of ::close_framegrabber is impossible).
Since all frame grabbers are closed by ::close_all_framegrabbers all frame grabber handles become invalid.
If it is possible to close the frame grabbers the operator ::close_all_framegrabbers returns the value H_MSG_TRUE. Otherwise an exception handling is raised.
Image / region / XLD management
