HOWTO: update ja_JP/HOWTO with latest changes

Here is another sync patch of Documentation/ja_JP/HOWTO

Japanese developer sent me some cosmetic changes and also follow
changes of HOWTO
    Cross reference URL (sosdg.org/qiyong/lxr)
    known_regression explanations on kernel dev. process
Signed-off-by: Tsugikazu Shibata <tshibata@ab.jp.nec.com>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>