Avoid garbled in "text" section.

Revert to English a few parts of "ja/in_forward.txt", because "text" section was garbled.
It seems that problem of except for the Translation.

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Please refer following commit and image.

commit: 
https://github.com/fluent/fluentd-docs/blob/c784726bc027cb9725dd712ccd396d2b79175537/docs/ja/in_forward.txt#L35-L45

image: 
![screen shot 2014-01-04 at 8 09 38 am](https://f.cloud.github.com/assets/194222/1843370/9f7dccc4-74cf-11e3-9419-9a021ac24656.png)