1. changed all "wxMBConv& conv" parameters to "const wxMBConv&"

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

src/common/ffile.cpp

@@ -103,7 +103,7 @@ bool wxFFile::Close()
 // read/write
 // ----------------------------------------------------------------------------
 
-bool wxFFile::ReadAll(wxString *str, wxMBConv& conv)
+bool wxFFile::ReadAll(wxString *str, const wxMBConv& conv)
 {
     wxCHECK_MSG( str, false, wxT("invalid parameter") );
     wxCHECK_MSG( IsOpened(), false, wxT("can't read from closed file") );