Makes issue custom fields available as timelog columns (#1766).

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@11174 e93f8b46-1217-0410-a6f0-8f06a7374b81
German translation updated by Daniel Felix (#12819)

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@11175 e93f8b46-1217-0410-a6f0-8f06a7374b81