Windows: Test for PRSFS_INSERT in redirector interface

If a test for PRSFS_WRITE fails and the cm_scache.creator is the
current user, then also test for PRSFS_INSERT privilege.

Change-Id: Ib3e34f7ce50216cd9ff82afe9a7184f79d46ce15
Reviewed-on: http://gerrit.openafs.org/8978
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: Jeffrey Altman <jaltman@your-file-system.com>