fix tag balancing logics

- logics simplified
- optional tags are ignored during balancing
- ignore self-closing solidus, which is required only for foreign
elements

Author: adon

tests/test-vectors.js

@@ -831,6 +831,16 @@ var generalVectors = [
 	id: 50,
 	input: "abc <!-- 123",
 	output: "abc "
+},
+{
+	id: 51,
+	input: "<img src=\"x\" id=\'\" onerror=\"alert(1)\' />",
+	output: "<img src=\"x\" id=\'\" onerror=\"alert(1)\' />"
+},
+{
+	id: 52,
+	input: "<a href='http://www.yahoo.com/' />hello",
+	output: "<a href='http://www.yahoo.com/'>hello</a>"
 }
 ];