Update classes/log.html
typo
installation/upgrade.html を修正
general/extending_core.htmlを一部翻訳
Update classes/log.html
validation/validation.html を一部翻訳
Merge pull request #278 from raben/1.6/develop_japanese

1.6/develop japanese
Merge pull request #279 from kenjis/fix_upgrade

installation/upgrade.html を修正
Merge pull request #280 from sharkpp/1.6/develop_japanese

general/extending_core.htmlを一部翻訳
Merge pull request #281 from tatsuyaueda/patch-3

validation/validation.html を一部翻訳