Windows: Use MountRoot for Absolute Symlinks

Windows: Use MountRoot for Absolute Symlinks

Replace the absolute symlink processing in AFSLocateName().
Implement AFSIsAbsoluteAFSName() to test whether or not the
path is in fact an absolute /afs path by comparing the input
string to the registry MountRoot value which specifies the
case sensitive root path for all absolute symlinks stored
in the AFS cell.

If a symlink target path begins with a directory separator
and is not an absolute afs path name, return an error.

Construct the substitution string using the target path
without the MountRoot prefix.

Add functionality to AFSRedir.sys to read the MountRoot
from the registry and pass it on to AFSRedirLib.sys.

Change-Id: Ie1df24da1e6de257c73dc34c80a75288bad47d29
Reviewed-on: http://gerrit.openafs.org/8353
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: Jeffrey Altman <jaltman@your-file-system.com>