Windows: fs chmod and display mode in fs examine

Windows: fs chmod and display mode in fs examine

Make use of the new pioctl VIOC_GETUNIXMODE and VIOC_SETUNIXMODE
operations to display the current mode in fs examine and permit
setting the mode with "fs chmod".   The mode string parsing makes
use of Vincent Archer's code from Minix.  The required copyright
statement and license is attached to parsemode().

afsconfig-windows.h gains definitions for various mode symbols
that are not defined by Visual Studio runtime headers.

Change-Id: I624f73154b7f177f93289e2641da5d9478ea931c
Reviewed-on: http://gerrit.openafs.org/3546
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Tested-by: Jeffrey Altman <jaltman@openafs.org>