Add test for nested comment block

integration-tests/templates/comment.out

@@ -0,0 +1 @@
+10001

integration-tests/templates/comment.stpl

@@ -0,0 +1 @@
+<%= 1 + /* 10 + %> /* 100 + */ 1000 %> + */ 10000 %>

integration-tests/tests/template_once.rs

@@ -164,6 +164,15 @@ fn test_rm_whitespace() {
     );
 }
 
+#[derive(TemplateOnce)]
+#[template(path = "comment.stpl")]
+struct Comment {}
+
+#[test]
+fn test_comment() {
+    assert_render("comment", Comment{})
+}
+
 #[cfg(unix)]
 mod unix {
     use super::*;