Configurable behavour for linking issues on copy (#18500).

git-svn-id: http://svn.redmine.org/redmine/trunk@13668 e93f8b46-1217-0410-a6f0-8f06a7374b81
Adds translation strings (#18500).

git-svn-id: http://svn.redmine.org/redmine/trunk@13669 e93f8b46-1217-0410-a6f0-8f06a7374b81