Fix problem with help not including parent command names for subcommands

lib/thor.rb

@@ -199,9 +199,14 @@ def printable_tasks(all = true, subcommand = false)
     def subcommands
       @subcommands ||= from_superclass(:subcommands, [])
     end
+
+    def parent_commands
+      @parent_commands ||= from_superclass(:parent_commands, [])
+    end
 
     def subcommand(subcommand, subcommand_class)
       self.subcommands << subcommand.to_s
+      subcommand_class.parent_commands << subcommand.to_s
       subcommand_class.subcommand_help subcommand
       define_method(subcommand) { |*args| invoke subcommand_class, args }
     end

lib/thor/task.rb

@@ -39,6 +39,9 @@ def formatted_usage(klass, namespace = true, subcommand = false)
 
       formatted ||= ""
 
+      # Add parent commands (for subcommands)
+      klass.parent_commands.each {|parent_command| formatted << parent_command + ' ' }
+
       # Add usage with required arguments
       formatted << if klass && !klass.arguments.empty?
         usage.to_s.gsub(/^#{name}/) do |match|