don't show assert message boxes in debug build but throw an exception if an assert...

don't show assert message boxes in debug build but throw an exception if an assert unexpectedly fails; do check that expected asserts are generated

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@57459 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775