Windows: Backup and restore configuration across installs

Windows: Backup and restore configuration across installs

The MSI installer for OpenAFS does not preserve configuration data
across installs.  This patch creates a backup of specific
configuration registry values when uninstalling OpenAFS and uses this
backup when subsequently installing OpenAFS.

Reviewed-on: http://gerrit.openafs.org/2977
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Tested-by: Jeffrey Altman <jaltman@openafs.org>
(cherry picked from commit 1418b4fec23459aafec4b5a787e2c2b89f6af1f1)
Change-Id: I4eab1a4a3ea33bdcd7ccb27aea0927eed16892ca
Reviewed-on: http://gerrit.openafs.org/3142
Tested-by: Derrick Brashear <shadow@dementia.org>
Reviewed-by: Derrick Brashear <shadow@dementia.org>