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

app/views/issues/_attributes.rhtml

@@ -7,7 +7,7 @@
 <p><label><%= l(:field_status) %></label> <%= @issue.status.name %></p>
 <% end %>
 
-<p><%= f.select :priority_id, (@priorities.collect {|p| [p.name, p.id]}), :required => true %></p>
+<p><%= f.select :priority_id, (@priorities.collect {|p| [p.name, p.id]}), {:required => true}, :disabled => !@issue.leaf? %></p>
 <p><%= f.select :assigned_to_id, (@issue.assignable_users.collect {|m| [m.name, m.id]}), :include_blank => true %></p>
 <% unless @project.issue_categories.empty? %>
 <p><%= f.select :category_id, (@project.issue_categories.collect {|c| [c.name, c.id]}), :include_blank => true %>
@@ -31,10 +31,10 @@
 </div>
 
 <div class="splitcontentright">
-<p><%= f.text_field :start_date, :size => 10 %><%= calendar_for('issue_start_date') %></p>
-<p><%= f.text_field :due_date, :size => 10 %><%= calendar_for('issue_due_date') %></p>
-<p><%= f.text_field :estimated_hours, :size => 3 %> <%= l(:field_hours) %></p>
-<% if Issue.use_field_for_done_ratio? %>
+<p><%= f.text_field :start_date, :size => 10, :disabled => !@issue.leaf? %><%= calendar_for('issue_start_date') if @issue.leaf? %></p>
+<p><%= f.text_field :due_date, :size => 10, :disabled => !@issue.leaf? %><%= calendar_for('issue_due_date') if @issue.leaf? %></p>
+<p><%= f.text_field :estimated_hours, :size => 3, :disabled => !@issue.leaf? %> <%= l(:field_hours) %></p>
+<% if @issue.leaf? && Issue.use_field_for_done_ratio? %>
 <p><%= f.select :done_ratio, ((0..10).to_a.collect {|r| ["#{r*10} %", r*10] }) %></p>
 <% end %>
 </div>