tar: Make x-option to extract no matter what format (bz2...)

[Jari Aalto]

It is very non-intuitive to have to apply a specific compression option
during the uncompress. It would be more user friendly to make "-x" option
to extract the file no matter what compression was used. Like:

   tar xvf this.tar.bz2
   tar xvf this.tar.gz
   tar xvf this.tar

If this is not possible, please add option "X", which would accomplich
this "Generic extraction". In shell scripts it would be much easier.

Further:

Tar could support any compression bethod with "X" option, so that it
could call external utilities like

      rzip          rzip.samba.org      
      lzop          www.lzop.org

in case the file extension were

   *.rz
   *.lzo

This could be easily added to the file extension detection routine
inside tar. It does not need to be built-in the binary.

Jari