Submitted by: Mike Pritchard <pritc003@maroon.tc.umn.edu>

msdosfs_lookup() did no validation to see if the caller was validated
to delete/rename/create files. msdosfs_setattr() did no validation
to see if the caller was allowed to change the file permissions (turn
on/off the write bit) or update the file modification time (utimes).

The routines were fixed to validate the calls just like ufs does.