Avoid duplicate wxEVT_COMMAND_TREE_SEL_CHANG{ING,ED} events in wxMSW.

When changing the selected item programmatically 2 CHANGING and CHANGED events
were sent because the assumption that comctl32.dll didn't send these events
itself was not correct any more, it does send them at least since XP. However
to avoid the tests for its exact version it's simpler to just ignore the
events it generates and continue sending our own ones.

Closes #11274.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@65906 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775