cifs-utils security, bug fix, and enhancement update

[4.8.1-10]

• mount.cifs: don’t allow unprivileged users to mount onto dirs they can’t chdir into (bz 812782)
  [4.8.1-9]
• cifs.upcall: use krb5_sname_to_principal to construct principal name (bz 805490)
  [4.8.1-8]
• mount.cifs: add backupuid=/backupgid= mount options (bz 806337)
  [4.8.1-7]
• RFE: Improve selection of SPNs with cifs.upcall (bz 748757)
• mount.cifs does not use KRB5_CONFIG (bz 748756)
  [creates additional entries in /etc/mtab (bz 770004)]
• mount.cifs does not honor the uid/gid=username option, only the uid/gid=# option (bz 796463)
  [4.8.1-6]
• undocumented mount.cifs options (bz 769923)