add missing "require 'diff'" to Redmine::Helpers::Diff (#15105)...
add missing "require 'diff'" to Redmine::Helpers::Diff (#15105)
Contributed by Felix Bünemann.
git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@12206 e93f8b46-1217-0410-a6f0-8f06a7374b81