New strings to localization (#5225)

* error_can_not_delete_custom_field: Unable to delete custom field
* error_unable_to_connect: Unable to connect ({{value}})
* error_can_not_remove_role: This role is in use and can not be deleted.
* error_can_not_delete_tracker: This tracker contains issues and can't be deleted.


git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@3627 e93f8b46-1217-0410-a6f0-8f06a7374b81

app/controllers/trackers_controller.rb

@@ -55,7 +55,7 @@ class TrackersController < ApplicationController
   def destroy
     @tracker = Tracker.find(params[:id])
     unless @tracker.issues.empty?
-      flash[:error] = "This tracker contains issues and can\'t be deleted."
+      flash[:error] = l(:error_can_not_delete_tracker)
     else
       @tracker.destroy
     end