fixed block inheritance with several levels

Tests/StencilTests/InheritenceSpec.swift

@@ -11,17 +11,17 @@ func testInheritence() {
 
     $0.it("can inherit from another template") {
       let template = try environment.loadTemplate(name: "child.html")
-      try expect(try template.render()) == "Header\nChild"
+      try expect(try template.render()) == "Super_Header Child_Header\nChild_Body"
     }
 
     $0.it("can inherit from another template inheriting from another template") {
       let template = try environment.loadTemplate(name: "child-child.html")
-      try expect(try template.render()) == "Child Child Header\nChild"
+      try expect(try template.render()) == "Super_Header Child_Header Child_Child_Header\nChild_Body"
     }
 
     $0.it("can inherit from a template that calls a super block") {
       let template = try environment.loadTemplate(name: "child-super.html")
-      try expect(try template.render()) == "Header\nChild Body"
+      try expect(try template.render()) == "Header\nChild_Body"
     }
   }
 }

Tests/StencilTests/fixtures/child-child.html

@@ -1,2 +1,2 @@
 {% extends "child.html" %}
-{% block header %}Child Child Header{% endblock %}
+{% block header %}{{ block.super }} Child_Child_Header{% endblock %}

Tests/StencilTests/fixtures/child-super.html

@@ -1,3 +1,3 @@
 {% extends "base.html" %}
-{% block body %}Child {{ block.super }}{% endblock %}
+{% block body %}Child_{{ block.super }}{% endblock %}
 

Tests/StencilTests/fixtures/child.html

@@ -1,2 +1,3 @@
 {% extends "base.html" %}
-{% block body %}Child{% endblock %}
+{% block header %}Super_{{ block.super }} Child_Header{% endblock %}
+{% block body %}Child_Body{% endblock %}