Failing test for fabpot/Twig#958

This test case reproduces the issue reported by @stof in fabfot/Twig#958. This
problem is being caused by the fact that the {% embed %} tag causes the
generation of a separate template class sharing the exact same
$this->templateName value as the main template containing the tag. This then
confuses Twig_Error::guessTemplateInfo when it's iterating through the
$backtrace comparing $this->filename to $trace['object']->getTemplateName().

test/Twig/Tests/Fixtures/tags/embed/error_line.test

@@ -0,0 +1,16 @@
+--TEST--
+"embed" tag
+--TEMPLATE(index.twig)--
+FOO
+{% embed "foo.twig" %}
+    {% block c1 %}
+        {{ nothing }}
+    {% endblock %}
+{% endembed %}
+BAR
+--TEMPLATE(foo.twig)--
+{% block c1 %}{% endblock %}
+--DATA--
+return array()
+--EXCEPTION--
+Twig_Error_Runtime: Variable "nothing" does not exist in "index.twig" at line 5