add test of attachment thumbnail etag

git-svn-id: http://svn.redmine.org/redmine/trunk@13175 e93f8b46-1217-0410-a6f0-8f06a7374b81
fix variable name confusion at AttachmentsController#thumbnail

This is suggested by Rails team.
https://github.com/rails/rails/issues/15471#issuecomment-45419147

git-svn-id: http://svn.redmine.org/redmine/trunk@13176 e93f8b46-1217-0410-a6f0-8f06a7374b81
fix Ruby Logger doc link (#5706)

git-svn-id: http://svn.redmine.org/redmine/trunk@13177 e93f8b46-1217-0410-a6f0-8f06a7374b81
Japanese translation updated by Go MAEDA (#17166)

git-svn-id: http://svn.redmine.org/redmine/trunk@13180 e93f8b46-1217-0410-a6f0-8f06a7374b81
Gemfile: pin request_store version 1.0.5 (#16685)

Many integration tests are broken.

git-svn-id: http://svn.redmine.org/redmine/trunk@13181 e93f8b46-1217-0410-a6f0-8f06a7374b81