Windows: AFSDeleteDirEntry set input to NULL

AFSDeleteDirEntry() frees the memory allocated to the DirectoryCB.
To ensure that an invalid memory pointer is not accidentally used
by the caller after the memory is freed, use
InterlockedCompareExchangePointer() to set the input parameter to
NULL prior to destroying the DirectoryCB.

Change-Id: I2e92d4277d1f9baee164bfb941821aa11a1ad738
Reviewed-on: http://gerrit.openafs.org/9721
Reviewed-by: Peter Scott <pscott@kerneldrivers.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: Jeffrey Altman <jaltman@your-file-system.com>
Windows: Switch to Interlocked ops for RDR Set/Clear

Switch to using interlocked operations for the SetFlag and ClearFlag
macros.

Change-Id: I2b071ae49f69d557c30d1280fb7877dde7f76f40
Reviewed-on: http://gerrit.openafs.org/9722
Reviewed-by: Peter Scott <pscott@kerneldrivers.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: Jeffrey Altman <jaltman@your-file-system.com>