Add a common tag for wxItemContainer-derived classes tests

This makes it possible to run the tests for all controls implementing
wxItemContainer interface by just passing "[item-container]" on the test
command line.

tests/controls/htmllboxtest.cpp

@@ -43,11 +43,8 @@ private:
     wxDECLARE_NO_COPY_CLASS(HtmlListBoxTestCase);
 };
 
-// register in the unnamed registry so that these tests are run by default
-CPPUNIT_TEST_SUITE_REGISTRATION( HtmlListBoxTestCase );
-
-// also include in its own registry so that these tests can be run alone
-CPPUNIT_TEST_SUITE_NAMED_REGISTRATION( HtmlListBoxTestCase, "HtmlListBoxTestCase" );
+wxREGISTER_UNIT_TEST_WITH_TAGS(HtmlListBoxTestCase,
+                               "[HtmlListBoxTestCase][item-container]");
 
 void HtmlListBoxTestCase::setUp()
 {