kes Modify disk changer to simulate some of the error conditions

kes  Modify disk changer to simulate some of the error conditions
     of mtx-changer.
kes  Make sure the close() call in the SD tools is just before the
     getchar() call.
kes  Implement dir_get_volume_info() in bls using the patch from
     Richard Mortimer but call find_num_dvd_parts().
kes  Implement find_num_dvd_parts() that mounts and scans a DVD
     and counts the parts.
kes  Move the omode code in open_dvd() up so that the cannot
     write on blank disk can check can be bypassed for read mode.
     Not yet implemented.

git-svn-id: https://bacula.svn.sourceforge.net/svnroot/bacula/trunk@3457 91ce42f0-d328-0410-95d8-f526ca767f89