add head method to repo and resolve method to references

includes associated unit tests

ext/rugged/rugged_reference.c

@@ -221,5 +221,6 @@ void Init_rugged_reference()
 	rb_define_method(rb_cRuggedReference, "name", rb_git_ref_name, 0);
 	rb_define_method(rb_cRuggedReference, "name=", rb_git_ref_rename, 1);
 
+	rb_define_method(rb_cRuggedReference, "resolve", rb_git_ref_resolve, 0);
 	rb_define_method(rb_cRuggedReference, "delete", rb_git_ref_delete, 0);
 }

lib/rugged/repository.rb

@@ -10,6 +10,11 @@ def walk(from, sorting=Rugged::SORT_DATE)
         yield commit
       end
     end
+
+    def head
+      ref = Reference.lookup(self, "HEAD")
+      ref.resolve
+    end
   end
 
 end

test/reference_test.rb

@@ -50,4 +50,15 @@
     assert_equal "5b5b025afb0b4c913b4c338a42934a3863bf3644", ref.target
     ref.delete
   end
+
+  test "can resolve head" do
+    ref = Rugged::Reference.lookup(@repo, "HEAD")
+    assert_equal "refs/heads/master", ref.target
+    assert_equal "tree", ref.type
+
+    head = ref.resolve
+    assert_equal "36060c58702ed4c2a40832c51758d5344201d89a", head.target
+    assert_equal "commit", head.type
+  end
+
 end

test/repo_test.rb

@@ -71,6 +71,12 @@
     assert list.map {|c| c.sha[0,5] }.join('.'), "a4a7d.c4780.9fd73.4a202.5b5b0.84960"
   end
 
+  test "can lookup head from repo" do
+    head = @repo.head
+    assert_equal "36060c58702ed4c2a40832c51758d5344201d89a", head.target
+    assert_equal "commit", head.type
+  end
+
   test "garbage collection methods don't crash" do
     Rugged::Repository.new(@path)
     ObjectSpace.garbage_collect