THRIFT-4763: HTML compiler produces invalid HTML document (#1720)

* HTML: the html generator did generate a closing </code> tag without a match <code>
* THRIFT-4763: added HTML test and fixed up additional HTML generation issues
diff --git a/test/Makefile.am b/test/Makefile.am
index 682e04a..f6b867c 100755
--- a/test/Makefile.am
+++ b/test/Makefile.am
@@ -103,10 +103,17 @@
 endif
 
 #
-# generate html for ThriftTest.thrift
+# generate html for ThriftTest.thrift AND validate it!
 #
+if WITH_NODEJS
 check-local:
 	$(top_builddir)/compiler/cpp/thrift --gen html -r $(top_srcdir)/test/ThriftTest.thrift
+	$(top_builddir)/node_modules/.bin/html-validator --file=gen-html/index.html --verbose
+	$(top_builddir)/node_modules/.bin/html-validator --file=gen-html/ThriftTest.html --verbose
+else
+check-local:
+	$(top_builddir)/compiler/cpp/thrift --gen html -r $(top_srcdir)/test/ThriftTest.thrift
+endif
 
 clean-local:
 	$(RM) -r $(top_srcdir)/test/gen-html/