NAME
	ParentDir -- Obtain the parent of a directory or file

    SYNOPSIS
	newlock = ParentDir( lock )
	D0		     D1

	 BPTR ParentDir( BPTR)

    FUNCTION
	The argument 'lock' is associated with a given file or directory.
	ParentDir() returns 'newlock' which is associated the parent
	directory of 'lock'.

	Taking the ParentDir() of the root of the current filing system
	returns a NULL (0) lock.  Note this 0 lock represents the root of
	file system that you booted from (which is, in effect, the parent
	of all other file system roots.)

    INPUTS
	lock - BCPL pointer to a lock

    RESULTS
	newlock - BCPL pointer to a lock

    SEE ALSO
	 Lock(),  DupLock(),  UnLock(),  ParentOfFH(),  DupLockFromFH()