Windows: store data verification mode

Windows: store data verification mode

Over the lifetime of OpenAFS a number of bugs have been discovered
that can result in data corruption.  This new mode (Windows only)
will double check that the data received by the file server does
in fact match the data that was written by the cache manager.

After a successful StoreData and status merge but before the BIOD
is released, a fetchdata is issued to read the data written by the
cache manager.  If the data fails to match, the StoreData operation
is repeated.

Data verification mode can be queried with "fs getverify" and set
with "fs setverify {on, off}".  The default value can be set with
the TransarcAFSDaemon\Parameters DWORD "VerifyData" registry value.

By default verification is disabled.

Change-Id: Ic99c1692e6e78790e65ae600c3e428a79df59370
Reviewed-on: http://gerrit.openafs.org/6601
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@secure-endpoints.com>
Tested-by: Jeffrey Altman <jaltman@secure-endpoints.com>