kes Correct a test in block.c that prevented restore of a DVD from

kes  Correct a test in block.c that prevented restore of a DVD from
     looking at the last part in the spool directory.
kes  Make some error messages clearer mostly by using the word DVD
     in the message. Improve infor message in read_record for DVDs.
kes  Remove DVD kludges in dircmd.c label/relabel.
kes  Move the dvd relabel code from dircmd.c into
     write_new_volume_label_to_dvd() adding a relabel argument.
kes  Rewrite the truncate_dvd() code to be much simpler and
     more logical. First blow away any spool part, then create a
     new empty part and write to the DVD.
kes  Rewrite the can_write_on_non_blank_dvd() code making it
     only ensure that no valid data is on the DVD -- i.e. it
     can be overwritten.

git-svn-id: https://bacula.svn.sourceforge.net/svnroot/bacula/trunk@3477 91ce42f0-d328-0410-95d8-f526ca767f89