[Merge] lp:~futatuki/mailman/2.1-ja-translation into lp:mailman/2.1

Yasuhito FUTATSUKI at POEM has proposed merging lp:~futatuki/mailman/2.1-ja-translation into lp:mailman/2.1.

Commit message: Update Japanese translation

Requested reviews: Mailman Coders (mailman-coders)

For more details, see: https://code.launchpad.net/~futatuki/mailman/2.1-ja-translation/+merge/37748...

* Add msgstr for msgid added in rev 1829, in Japansese po file * also, add translated comment for new setting in Japanse translation of Defaults.py.in