. added checks for buffer sizes in sys_datacopy() functions in mfs,

. added checks for buffer sizes in sys_datacopy() functions in mfs,
  print debug message if copy is truncated
. increased buffer in lookup() to be PATH_MAX instead of NAME_MAX
. sanity check in fetch_name() in vfs to see if name fits, and
  is null-terminated
. first check i < NAME_MAX, then string[i] in search_dir, as we're
  not supposed to look at string[NAME_MAX]