xml_name_type() should report namespace error if name ends with colon

This means that either there is a non-qualified name colon, or no local name. The WPT tests expect
a NAMESPACE_ERR to be thrown, so this blocks servo#2185 to some degree

src/components/script/dom/bindings/utils.rs

@@ -704,6 +704,7 @@ pub fn xml_name_type(name: &str) -> XMLName {
     let mut iter = name.chars();
     let mut non_qname_colons = false;
     let mut seen_colon = false;
+    let mut was_colon = false;
     match iter.next() {
         None => return InvalidXMLName,
         Some(c) => {
@@ -721,13 +722,20 @@ pub fn xml_name_type(name: &str) -> XMLName {
             return InvalidXMLName;
         }
         if c == ':' {
+            was_colon = true;
             match seen_colon {
                 true => non_qname_colons = true,
                 false => seen_colon = true
             }
+        } else {
+            was_colon = false;
         }
     }
 
+    if was_colon {
+        return Name;
+    }
+
     match non_qname_colons {
         false => QName,
         true => Name