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/choicetest.cpp

@@ -45,11 +45,8 @@ private:
     wxDECLARE_NO_COPY_CLASS(ChoiceTestCase);
 };
 
-// register in the unnamed registry so that these tests are run by default
-CPPUNIT_TEST_SUITE_REGISTRATION( ChoiceTestCase );
-
-// also include in its own registry so that these tests can be run alone
-CPPUNIT_TEST_SUITE_NAMED_REGISTRATION( ChoiceTestCase, "ChoiceTestCase" );
+wxREGISTER_UNIT_TEST_WITH_TAGS(ChoiceTestCase,
+                               "[ChoiceTestCase][item-container]");
 
 void ChoiceTestCase::setUp()
 {