Warn user that subprojects are also deleted when deleting a project (#1111) and add a checkbox to confirm the deletion.

git-svn-id: http://redmine.rubyforge.org/svn/trunk@1359 e93f8b46-1217-0410-a6f0-8f06a7374b81

lang/en.yml

@@ -557,6 +557,7 @@ text_select_mail_notifications: Select actions for which email notifications sho
 text_regexp_info: eg. ^[A-Z0-9]+$
 text_min_max_length_info: 0 means no restriction
 text_project_destroy_confirmation: Are you sure you want to delete this project and related data ?
+text_subprojects_destroy_warning: 'Its subproject(s): %s will be also deleted.'
 text_workflow_edit: Select a role and a tracker to edit the workflow
 text_are_you_sure: Are you sure ?
 text_journal_changed: changed from %s to %s