Fix PKCS12 backup so that it works on the Mac. Use
nsILocalFile::OpenNSPRFileDesc to get a PRFileDesc*
instead of PR_Open since PR_Open doesn't deal with
native paths on the Mac at all.
git-svn-id: svn://10.0.0.236/trunk@98246 18797224-902f-48f8-a5cc-f745e15eee43