smartctl: Rework ataPrintMain(). Issue ATA SMART commands only if

necessary.  Improve handling of SMART STATUS command failure when ATA
output registers are missing (ticket #27).

git-svn-id: https://smartmontools.svn.sourceforge.net/svnroot/smartmontools/trunk@3081 4ea69e1a-61f1-4043-bf83-b5c94c648137