Updated Japanese translation for engine.ja.po.
Looks a bit weird seeing "Nihongo", "Japanese" is far more appropriate. "日本語" would be even better, but loading a larger font just for that seems a little bit of a waste.
Merge pull request #489 from Paul-Wortmann/master

Updated Japanese translation for engine.ja.po.
Merge pull request #486 from dorkster/bugfixes

Enable some menus when transformed
Allow specifying a range for item/currency loot
This obsoletes the hardcoded gold drops amounts by level for enemies.
Fix bonus_currency
Need sleep
Only show one tooltip context at a time

Closes #491

Tooltips can either be in the context of the map (events and NPCs), or
in the context of menus. Menu tooltips will always take priority over
map tooltips.