* fhandler.h (fhandler_dev_mem): Add methods mmap, munmap and msync.

    * fhandler.h (fhandler_dev_mem): Add methods mmap, munmap and msync.
        Add `unit' member.
        * fhandler_mem.cc (fhandler_dev_mem): Initialize `unit' as well.
        (init): Care for differences between /dev/mem, /dev/kmem (not
        implemented yet) and /dev/port.
        (open): Change debug message to reflect the device.
        (mmap): New function.
        (munmap): Ditto.
        (msync): Ditto.
        (fstat): Use unit when setting st_dev in stat structure.
        * mmap.cc (mmap): Handle MAP_ANONYMOUS flag.
        Change error handling slightly.
        * path.cc (get_device_number): Handle /dev/port.