Fix #11: Use DOM to determine actual namespace of current element

tests/dump-output/issue-11

@@ -0,0 +1,11 @@
+SimpleXML object (1 item)
+[
+	Element {
+		Name: 'notinnamespace'
+		String Content: ''
+		Content in Namespace test
+			Namespace URI: 'http://example.com'
+			Children: 0
+			Attributes: 1 - 'isinnamespace'
+	}
+]

tests/input/issue-11.xml

@@ -0,0 +1,2 @@
+<?xml version="1.0" standalone="yes"?>
+<notinnamespace xmlns:test="http://example.com" test:isinnamespace="true" />

tests/tree-output/issue-11

@@ -0,0 +1,4 @@
+SimpleXML object (1 item)
+[0] // <notinnamespace>
+	->attributes('http://example.com')
+		->isinnamespace