Rails4: replace hard-coded html with class at ApplicationHelperTest#test_redmine_links_with_a_different_project_before_current_project

See r12784 comment.

git-svn-id: http://svn.redmine.org/redmine/trunk@12806 e93f8b46-1217-0410-a6f0-8f06a7374b81
use escaped "Can't" constant at ApplicationHelperTest

git-svn-id: http://svn.redmine.org/redmine/trunk@12807 e93f8b46-1217-0410-a6f0-8f06a7374b81