abandon attempts to make wxAnyStrPtr behave as bool: user-defined logical operators...

abandon attempts to make wxAnyStrPtr behave as bool: user-defined logical operators don't short circuit silently breaking existing code so it is better to not provide them at all; instead simply return bool from the new versions taking wxString::const_iterator; advise to use the new versions in the new code and so in our own files

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@59829 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775