Ensure namespace-aware “clear the stack” handling

This change ensures that for all cases with spec requirements in the
form “clear the stack back to a foo context” — which involves checking
for elements with particular names — we only look for elements in the
HTML namespace, rather than additionally looking for elements which
aren’t in the HTML namespace but that also have those particular names.

Otherwise, without this change, we aren’t in conformance with the spec
requirements, and we fail several cases in the html5lib-tests suite.

Fixes #33

Author: sideshowbarker

src/nu/validator/htmlparser/impl/TreeBuilder.java

@@ -3898,8 +3898,9 @@ private void endTagTemplateInHead() throws SAXException {
 
     private int findLastInTableScopeOrRootTemplateTbodyTheadTfoot() {
         for (int i = currentPtr; i > 0; i--) {
-            if (stack[i].getGroup() == TreeBuilder.TBODY_OR_THEAD_OR_TFOOT ||
-                    stack[i].getGroup() == TreeBuilder.TEMPLATE) {
+            if (stack[i].ns == "http://www.w3.org/1999/xhtml"
+                    && (stack[i].getGroup() == TreeBuilder.TBODY_OR_THEAD_OR_TFOOT
+                            || stack[i].getGroup() == TreeBuilder.TEMPLATE)) {
                 return i;
             }
         }
@@ -4667,7 +4668,7 @@ private int findLastOrRoot(@Local String name) {
 
     private int findLastOrRoot(int group) {
         for (int i = currentPtr; i > 0; i--) {
-            if (stack[i].getGroup() == group) {
+            if (stack[i].ns == "http://www.w3.org/1999/xhtml" && stack[i].getGroup() == group) {
                 return i;
             }
         }