added #parent_group method to Label and Key objects

spec/key_spec.rb

@@ -73,4 +73,10 @@ describe Redistat::Key do
     key.groups.map { |k| k.label }.should == result
   end
   
+  it "should know it's parent label group" do
+    label = 'message/public/offensive'
+    key = Redistat::Key.new(@scope, label, @date, {:depth => :hour})
+    key.parent_group.should == 'message/public'
+  end
+  
 end

spec/label_spec.rb

@@ -45,4 +45,10 @@ describe Redistat::Label do
     label.groups.should == [ "message" ]
   end
   
+  it "should know it's parent label group" do
+    name = "message/public/offensive"
+    label = Redistat::Label.new(name)
+    label.parent_group.should == 'message/public'
+  end
+  
 end