2. this allows to use wxConvAuto() instead of wxConvUTF8 as default value
for this parameter in the classes which read text from the file: wxConvAuto
automatically recognizes the BOM at the start of file and uses the correct
conversion
3. don't use Windows for UTF-7 conversions as there is no way to make it
fail on invalid UTF-7 strings; use our own wxMBConvUtf7 instead
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@38570 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
