Update to 2.4.7
    
    - drop some no-longer-necessary code to cede ownership of keyring ccaches
      to an unprivileged user at login-time to work better with upcoming changes
      to libkrb5's keyring ccache support (libkrb5: #991148, this one's #1005376)
    - if we don't have a ccname_template, if we're built against a libkrb5 that
      provides interfaces for reading its configuration files, try to read the
      default_ccache_name value from the [libdefaults] section before falling
      back to the default we've set at compile-time (#more of #1005376)
    - stop specifying a default ccache location at compile-time on F21 and later,
      to make our unconfigured default better line up with libkrb5's unconfigured
      default