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.

archival/libunarchive/get_header_tar.c

@@ -65,7 +65,7 @@ extern char get_header_tar(archive_handle_t *archive_handle)
 
 	/* If there is no filename its an empty header */
 	if (tar.formated.name[0] == 0) {
-		return(EXIT_SUCCESS);
+		return(EXIT_FAILURE);
 	}
 
 	/* Check header has valid magic, "ustar" is for the proper tar