vol: Windows requires binary fmode for salvaged

vol: Windows requires binary fmode for salvaged

Same as 98f633c60d20834cee0bbc0770a3146b06642a59, but for the
salvageserver.

Reviewed-on: http://gerrit.openafs.org/3676
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Tested-by: Jeffrey Altman <jaltman@openafs.org>
(cherry picked from commit 802899aac022ab537159f3cd4435d072b5edc4be)

Change-Id: I953a780f61ce377179829d4e42e9aab76b3a8f4d
Reviewed-on: http://gerrit.openafs.org/3835
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>