Make TreeTester ignore tests for keygen element

This change makes TreeTester ignore any tests which have the keygen
element in their expected results.

Otherwise, without this change, we fail the tokenizer test at
https://github.com/html5lib/html5lib-tests/blob/master/tree-construction/tests7.dat#L409
due to the fact with 8f9f6bc
we completely removed keygen parsing support from our code. (However,
the keygen parsing requirements are still in the HTML spec, so the test
case cannot be removed from html5lib-tests.)

Author: sideshowbarker

test-src/nu/validator/htmlparser/test/TreeTester.java

@@ -213,6 +213,9 @@ private boolean runTest() throws Throwable {
                 expectedBuilder.append((char)ch);
             }
             String expected = expectedBuilder.toString();
+            if (expected.contains("<keygen>")) {
+                return true;
+            }
             String actual = sw.toString();
 
             LinkedList<String> actualErrors = leh.getErrors();