Log Message:
Update ja-squirrelmail package to 1.4.8.

Changes from 1.4.7:
- A security fix for CVE-2006-4019
- A collection of bugfixes

Changes from 1.4.6:
- Fixed URL for Read Receipts being incorrect in some cases (#1177518).
- Fixed endless loop when trying to parse "From: )(" (#1517867).
- Using is_file() instead of file_exists() in fortune plugin (#1499134).
- Add manual page for conf.pl under contrib.
- Don't allow selecting INBOX as Sent, Draft or Trash folder (#1242346).

Todo:
Make squirrelmail-decode and squirrelmail-locale depend on ja-squirrelmail
as well as squirrelmail.