Add 2 builtin words for working with directories:
	isdir?		( fd -- bool )
	freaddir	( fd -- ptr len TRUE | FALSE )

The 'isdir?' word returns `true' if the file descriptor is for a
directory and `false' otherwise.

The 'freaddir' word reads the next directory entry and if successful,
returns its name and 'true'. Otherwise 'false' is returned.

These words give the loader the ability to scan directories and read
files contained in them for 'rc.d'-like flexibility in handling which
modules to load and/or which tunables to set.

Obtained from:	Juniper Networks, Inc.
Implement 1003.1-2001 pathconf() keys.

This is based on r106058 in UFS.

MFC after:	1 month
Add John Marino to committers-port.dot

Approved by:	bapt (mentor)