Windows: Rewrite LargeSearchTime conversions

Use LARGE_INTEGER to avoid the need for shifting and DWORD casts.
Take into account the size of time_t.

Reviewed-on: http://gerrit.openafs.org/10673
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
(cherry picked from commit da7adce6dddd39eb151576abfb1681c559e1e4e5)

Change-Id: I633ec1e9da5820bbb1f5d30a3854c7e906027602
Reviewed-on: http://gerrit.openafs.org/10674
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>