Adds subtasking (#443) including:

* priority, start/due dates, progress, estimate, spent time roll-up to parent issues
* descendant issues tree displayed on the issue view with context menu support
* issue tree display on the gantt chart
* issue tree copy on project copy
* unlimited nesting

Defining subtasks requires the new permission 'Manage subtasks'.
Subtasks can not belong to a different project than the parent task.

Implementation is based on scoped nested sets for fast reads and updates.

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@3573 e93f8b46-1217-0410-a6f0-8f06a7374b81

public/javascripts/application.js

@@ -194,6 +194,18 @@ function randomKey(size) {
 	return key;
 }
 
+function observeParentIssueField(url) {
+  new Ajax.Autocompleter('issue_parent_issue_id',
+                         'parent_issue_candidates',
+                         url,
+                         { minChars: 3,
+                           frequency: 0.5,
+                           paramName: 'q',
+                           updateElement: function(value) {
+                             document.getElementById('issue_parent_issue_id').value = value.id;
+                           }});
+}
+
 /* shows and hides ajax indicator */
 Ajax.Responders.register({
     onCreate: function(){