Windows: AFSCommonWrite add bWriteToEndOfFile var

To improve readability add a bWriteToEndOfFile variable which
stores the value of

  liStartingByte.LowPart == FILE_WRITE_TO_END_OF_FILE &&
  liStartingByte.HighPart == -1

Reviewed-on: http://gerrit.openafs.org/11068
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
(cherry picked from commit 564f9fd06777882abd29a0da6274150f5b1e7d7f)

Change-Id: Id156545870759b77eccc0ca27e7c9a013611db8d
Reviewed-on: http://gerrit.openafs.org/11079
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Windows: Pin write position prior to defer

If we extend the file prior to defrring the write *and* the write
is set up FILE_WRITE_TO_END_OF_FILE then we have to convert the
FILE_WRITE_TO_END_OF_FILE to an absolute position since we have
already moved the FCB->Header.FileSize.

Reviewed-on: http://gerrit.openafs.org/11069
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Rod Widdowson <rdw@steadingsoftware.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
(cherry picked from commit a4bcc4b1dccf6ab2745be83288c380f5454a2db9)

Change-Id: I80bcb6caf7be7edd760b879cc567602346138d1a
Reviewed-on: http://gerrit.openafs.org/11080
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>