Fix TreeCtrlTestCase assert failure under Windows.

A '-' keypress doesn't collapse a tree item with the native MSW tree
control. Instead, when not using the generic tree control, simulate a
keypress of WXK_LEFT to collapse the root item . This fixes the assert
checking if the root item is collapsed after the keypress.

Regression since 9d7a7ec556 (which
mistakenly may have had treectrltest.cpp as part of its commit).

tests/controls/treectrltest.cpp

@@ -587,7 +587,12 @@ void TreeCtrlTestCase::KeyNavigation()
 
     CPPUNIT_ASSERT(m_tree->IsExpanded(m_root));
 
+#ifdef wxHAS_GENERIC_TREECTRL
     sim.Char('-');
+#else
+    sim.Char(WXK_LEFT);
+#endif
+
     wxYield();
 
     CPPUNIT_ASSERT(!m_tree->IsExpanded(m_root));