* fhandler.h (class fhandler_dev_tape): Add declaration for

	* fhandler.h (class fhandler_dev_tape): Add declaration for
	fixup_after_fork and set_close_on_exec.
	* fhandler_tape.cc (fhandler_dev_tape::open): Create mt_mtx mutex
	inheritable.
	(fhandler_dev_tape::close): Close mt_mtx.
	(fhandler_dev_tape::dup): Duplicate mt_mtx and mt_evt as necessary.
	(fhandler_dev_tape::fixup_after_fork): New method.
	(fhandler_dev_tape::set_close_on_exec): New method.