Replaced acronym with abbr tags (#15191).

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@12235 e93f8b46-1217-0410-a6f0-8f06a7374b81
Prevents duplicate element ids (#15191).

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@12236 e93f8b46-1217-0410-a6f0-8f06a7374b81