Add test for Push/PopStatusText().

Add test for Push/PopStatusText().

Allow to interactively push and pop status messages for the selected field.

This shows that currently PushStatusText() is completely broken under wxMSW
as it never shows the text being pushed at all because it is "optimized" away
due to an incorrect comparison with the old value (which turns out to be the
new one)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@61622 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775