Fix problem with help not including parent command names for subcommands

See problem identified in github Issue 128. This patch has been submitted
as Issue 137

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/group.rb

@@ -203,6 +203,10 @@ def printable_tasks(*)
       item << (desc ? "# #{desc.gsub(/\s+/m,' ')}" : "")
       [item]
     end
+
+    def parent_commands
+      []
+    end
 
     def handle_argument_error(task, error) #:nodoc:
       raise error, "#{task.name.inspect} was called incorrectly. Are you sure it has arity equals to 0?"

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|

spec/task_spec.rb

@@ -13,18 +13,21 @@ def task(options={})
     it "includes namespace within usage" do
       Object.stub!(:namespace).and_return("foo")
       Object.stub!(:arguments).and_return([])
+      Object.stub!(:parent_commands).and_return([])
       task(:bar => :required).formatted_usage(Object).should == "foo:can_has --bar=BAR"
     end
 
     it "removes default from namespace" do
       Object.stub!(:namespace).and_return("default:foo")
       Object.stub!(:arguments).and_return([])
+      Object.stub!(:parent_commands).and_return([])
       task(:bar => :required).formatted_usage(Object).should == ":foo:can_has --bar=BAR"
     end
 
     it "injects arguments into usage" do
       Object.stub!(:namespace).and_return("foo")
       Object.stub!(:arguments).and_return([ Thor::Argument.new(:bar, nil, true, :string) ])
+      Object.stub!(:parent_commands).and_return([])
       task(:foo => :required).formatted_usage(Object).should == "foo:can_has BAR --foo=FOO"
     end
   end