Fixup the copy rule for win32

Windows accept that you use / in the filename, but some commands
in a dos shell use /option causing the shell to print an error
if it finds / in the path instead of \.

Change-Id: I1de003c32b025307fe6482913c798b77489e262e
Reviewed-on: http://review.couchbase.org/44184
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Dave Rigby <daver@couchbase.com>