Revert changes in the procedure taking the user's login

 - cuserid returns the effective user's name which is always root
 - getlogin_r seems not to work properly when changing users through su
   for instance (su user1)

   Related to issues #1 and possibly #9
Use only tar (cjvf) for both the archiving and the compression
No more movetar

Write directly to the destination, don't use temp files and then move.
This comes at the cost of possible left overs in a case of a fail (and
reduced turnins for the corresponding user).