* fhandler.h (struct part_t): New type.

	* fhandler.h (struct part_t): New type.
	(class fhandler_dev_floppy): Convert partitions to part_t pointer.
	Add lock_partition method.
	* fhandler_floppy.cc (fhandler_dev_floppy::lock_partition): New method
	to implement ondemand partition locking.
	(fhandler_dev_floppy::write_file): Call lock_partition from here if
	writing failed due to a potential write restriction on a disk
	partition.
	(fhandler_dev_floppy::open): Don't lock partitions here.
	(fhandler_dev_floppy::close): Keep track of partition handle reference
	count.  Close handles and remove partitions pointer ony if count is 0.
	(fhandler_dev_floppy::dup): Just copy partitions pointer and increment
	reference count.