NAME
	CurrentDir -- Make a directory lock the current directory

    SYNOPSIS
	oldLock = CurrentDir( lock )
	D0		      D1

	 BPTR CurrentDir( BPTR)

    FUNCTION
	CurrentDir() causes a directory associated with a lock to be made
	the current directory.	The old current directory lock is returned.

	A value of zero is a valid result here, this 0 lock represents the
	root of file system that you booted from.

	Any call that has to  Open() or  Lock() files (etc) requires that
	the current directory be a valid lock or 0.

    INPUTS
	lock - BCPL pointer to a lock

    RESULTS
	oldLock - BCPL pointer to a lock

    SEE ALSO
	 Lock(),  UnLock(),  Open(),  DupLock()