Windows: Adjust Last Write time handling for -1

Windows: Adjust Last Write time handling for -1

The "what date/time gets changed when and by whom" in Windows is badly
defined, but all filesystems support the semantic that if a date is set
using a specific file object (or the timestamp is set to the magic number
-1)
then other changes provoked by that file object will be ignored.

AFS redirector timestamp handling does not support this behavior.
For the LastWrite timestamp (other timestamps are pretty much advisory and
maintained on a best effort basis) the timestamp would be updated by a
write operation even after -1 is set via the file handle.

This patchset implements the -1 behavior for LastWrite.  It also follows
the standard Windows practice of setting the LastWrite timestamp to be the
time of close of the handle that performed the write, not the time of the
write itself.

Finally, it should be noted that since RX*FS_StoreXXX operations update
the last write time on the server the client must restore the LastWrite
timestamp at handle close if -1 was specified.

Change-Id: Ica0c566fabb6b3046eb51f827402d622190daea8
Reviewed-on: http://gerrit.openafs.org/11110
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>