Move from read_gz to the pipe()+fork() method.

open_transformer(), common code for pipe+fork.
Function pointer for read() no longer needed.
Allow inflate to be initialised with a specified buffer size to avoid
over-reading.
Reset static variables in inflate_get_next_window to fix a bug where
only the first file in a .zip would be be extracted.

archival/rpm2cpio.c

@@ -96,10 +96,9 @@ extern int rpm2cpio_main(int argc, char **argv)
 	}
 
 	check_header_gzip(rpm_fd);
-	if (inflate(rpm_fd, fileno(stdout)) != 0) {
+	if (inflate_gunzip(rpm_fd, fileno(stdout)) != 0) {
 		bb_error_msg("Error inflating");
 	}
-	check_trailer_gzip(rpm_fd);
 
 	close(rpm_fd);