Fix tar -j support

Fix tar -j support
Use the old fork() method of tar compression support, rather than
read_bz2....
 - (*uncompress)(int in, int out) seems like a more natural interface
for compression code.
 - it might improve performance by seperating the work into one cpu
bound and one io bound process.
 - There is extra code required to do read_[gz|bunzip] since (*uncompress)(int in,
int out) will normally be used by the standalone compression applet.

There have been problems with this method so if you see a "Short read"
error let me know.